Tarrant Regional Water Dist. v. Herrmann

(Slip Opinion) OCTOBER TERM, 2012 1

Syllabus

NOTE: Where it is feasible, a syllabus (headnote) will be released, as is
being done in connection with this case, at the time the opinion is issued.
The syllabus constitutes no part of the opinion of the Court but has been
prepared by the Reporter of Decisions for the convenience of the reader.
See United States v. Detroit Timber & Lumber Co., 200 U. S. 321, 337.

SUPREME COURT OF THE UNITED STATES

Syllabus

TARRANT REGIONAL WATER DISTRICT v.

HERRMANN ET AL.

CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR
THE TENTH CIRCUIT

No. 11–889. Argued April 23, 2013—Decided June 13, 2013
The Red River Compact (or Compact) is a congressionally sanctioned
agreement that allocates water rights within the Red River basin
among the States of Oklahoma, Texas, Arkansas, and Louisiana.
The area it governs is divided into five separate subdivisions called
“Reaches,” each of which is further divided into smaller “subbasins.”
At issue here are rights under the Compact to water located in Okla-
homa’s portion of Reach II, subbasin 5. In Reach II, the Compact—
recognizing that Louisiana lacks suitable reservoir sites to store wa-
ter during high flow periods and that the upstream States (Texas,
Oklahoma, and Arkansas) were unwilling to release their own stored
water for the benefit of a downstream State—granted control over
the water in four upstream subbasins (subbasins 1 through 4) to the
States in which each subbasin is located and required that water in a
fifth subbasin, subbasin 5, be allowed to flow to Louisiana at certain
minimum levels. Section 5.05(b)(1) of the Compact gives the States
“equal rights” to the use of subbasin 5’s waters when the flow is 3,000
cubic feet per second (CFS) or more, “provided no state is entitled to
more than 25 percent of the water in excess of 3,000 [CFS].” Under
the Compact, States are also entitled to continue with their intra-
state water administration.
Petitioner Tarrant Regional Water District (Tarrant) is a Texas
state agency responsible for providing water to north-central Texas
and its rapidly growing population. After unsuccessfully attempting
to purchase water from Oklahoma and others, Tarrant sought a wa-
ter resource permit from the Oklahoma Water Resources Board
(OWRB), respondents here, to take surface water from a tributary of
the Red River at a point located in Oklahoma’s portion of subbasin 5
2 TARRANT REGIONAL WATER DIST. v. HERRMANN

Syllabus

of Reach II. Knowing that the OWRB would likely deny its permit
application because of Oklahoma water laws that effectively prevent
out-of-state applicants from taking or diverting water from within
Oklahoma’s borders, Tarrant filed suit in federal court simultaneous-
ly with its permit application, seeking to enjoin the OWRB’s enforce-
ment of the state statutes on grounds that they were pre-empted by
federal law in the form of the Compact and violated the Commerce
Clause by discriminating against interstate commerce in water. The
District Court granted summary judgment for the OWRB, and the
Tenth Circuit affirmed.
Held:
1. The Compact does not pre-empt the Oklahoma water statutes.
Pp. 9–22.
(a) Tarrant claims that §5.05(b)(1) creates a borderless common
in subbasin 5 in which each of the signatory States may cross each
other’s boundaries to access a shared pool of water. Tarrant observes
that §5.05(b)(1)’s “equal rights” language grants each State an equal
entitlement to subbasin 5’s waters, subject to a 25 percent cap, and
argues that its silence concerning state lines indicates that the Com-
pact’s drafters did not intend the provision to allocate water accord-
ing to state borders. The OWRB counters that §5.05(b)(1)’s “equal
rights” afford each State an equal opportunity to use subbasin 5’s ex-
cess water within each State’s own borders, but that its silence on
cross-border rights indicates that the Compact’s drafters had no in-
tention to create any such rights in the signatory States. Pp. 9–11.
(b) Because interstate compacts are construed under contract-
law principles, see Texas v. New Mexico, 482 U. S. 124, 128, the Court
begins by examining the Compact’s express terms as the best indica-
tion of the parties’ intent. However, §5.05(b)(1)’s silence is, at the
very least, ambiguous regarding cross-border rights under the Com-
pact, so the Court turns to other interpretive tools to shed light on
the drafters’ intent. Three things persuade the Court that the Com-
pact did not grant cross-border rights: the well-established principle
that States do not easily cede their sovereign powers; the fact that
other interstate water compacts have treated cross-border rights ex-
plicitly; and the parties’ course of dealing. Pp. 11–22.
(1) The sovereign States possess an “absolute right to all their
navigable waters and the soils under them for their own common
use.” Martin v. Lessee of Waddell, 16 Pet. 367, 410. So, for example,
“ ‘[a] court deciding a question of title to [a] bed of navigable water
[within a State’s boundaries] must . . . begin with a strong presump-
tion’ against defeat of a State’s title.” United States v. Alaska, 521
U. S. 1, 34. It follows, then, that “[i]f any inference at all is to be
drawn from” silence in compacts touching on the States’ authority to
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Syllabus

control their waters, “it is that each State was left to regulate the ac-
tivities of her own citizens.” Virginia v. Maryland, 540 U. S. 56, 67.
Tarrant contends that §5.05(b)(1)’s silence infers that the signatory
States dispensed with the core state prerogative to control water
within its borders. But since States rarely relinquish their sovereign
powers, the better understanding is that there would be a clear indi-
cation of such devolution, not inscrutable silence. Tarrant counters
that its interpretation would not intrude on any sovereign preroga-
tive of Oklahoma, which would retain its authority to regulate the
water within its borders. But adopting Tarrant’s reading would nec-
essarily entail assuming that Oklahoma and three other States si-
lently surrendered substantial control over their waters when they
agreed to the Compact. Pp. 14–16.
(2) Looking to the customary practices employed in other inter-
state compacts also helps in ascertaining the parties’ intent. See,
e.g., Alabama v. North Carolina, 560 U. S. 330, ___. Many compacts
feature unambiguous language permitting signatory States to cross
each other’s borders to fulfill obligations under the compacts, and
many provide for the terms and mechanics of how such relationships
will operate. The absence of comparable provisions in the Red River
Compact strongly suggests that cross-border rights were never in-
tended to be part of the agreement. Tarrant claims that not all inter-
state compacts have such explicit language, but cites only one such
compact, and even it sets out a detailed scheme that would apply to
any contemplated diversions. Similarly, even if §2.05(d) of the Com-
pact, which gives “[e]ach Signatory State . . . the right to” “[u]se the
bed and banks of the Red River and its tributaries to convey stored
water, imported or exported water, and water apportioned according
to this Compact,” is read to establish cross-border diversions, it does
so through express language, not through an inference from silence.
Pp. 16–20.
(3) The parties’ conduct under the Compact also undermines
Tarrant’s position. See Alabama v. North Carolina, 560 U. S., at ___.
Once the Compact was approved in 1980, no signatory State pressed
for a cross-border diversion until Tarrant filed suit in 2007. And Tar-
rant’s earlier offer to purchase water from Oklahoma was a strange
decision if Tarrant believed the Compact entitled it to demand water
without payment. Nor is there any indication that Tarrant, any oth-
er Texas agency, or Texas itself previously made any mention of
cross-border rights within the Compact; and none of the other signa-
tory States has ever made such a claim. P. 20.
(4) Tarrant’s remaining arguments—that its interpretation is
necessary to realize the “structure and purpose of Reach II”; and that
§5.05(b)(1)’s 25 percent cap on each State’s access to subbasin 5’s ex-
4 TARRANT REGIONAL WATER DIST. v. HERRMANN

Syllabus

cess water implies that if a State cannot access sufficient water with-
in its borders to meet the cap, it must be able to cross borders to
reach that water—are unpersuasive. Pp. 20–22.
2. The Oklahoma water statutes also do not run afoul of the Com-
merce Clause. Tarrant claims that the statutes discriminate against
interstate commerce by preventing water left unallocated under the
Compact from being distributed out of State. But Tarrant’s assump-
tion that some water is left “unallocated” is incorrect. The interpre-
tive comment for Article V of the Compact makes clear that when the
flow is above 3,000 CFS, “all states are free to use whatever amount
of water they can put to beneficial use,” subject to the requirement
that if the amount of available water cannot satisfy all of those uses,
“each state will honor the other’s right to 25% of the excess flow.” If
more than 25 percent of subbasin 5’s water is located in Oklahoma,
that water is not “unallocated”; rather, it is allocated to Oklahoma
unless and until another State calls for an accounting and Oklahoma
is asked to refrain from utilizing more than its entitled share.
Pp. 22–24.
656 F. 3d 1222, affirmed.

SOTOMAYOR, J., delivered the opinion for a unanimous Court.
 Cite as: 569 U. S. ____ (2013) 1

Opinion of the Court

NOTICE: This opinion is subject to formal revision before publication in the
preliminary print of the United States Reports. Readers are requested to
notify the Reporter of Decisions, Supreme Court of the United States, Wash-
ington, D. C. 20543, of any typographical or other formal errors, in order
that corrections may be made before the preliminary print goes to press.

SUPREME COURT OF THE UNITED STATES
_________________

No. 11–889
_________________

TARRANT REGIONAL WATER DISTRICT,

PETITIONER v. RUDOLF JOHN

HERRMANN ET AL.

ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF

APPEALS FOR THE TENTH CIRCUIT

[June 13, 2013]

JUSTICE SOTOMAYOR delivered the opinion of the Court.
The Red River Compact, (or Compact), 94 Stat. 3305,
allocates water rights among the States within the Red
River basin as it winds through Texas, Oklahoma, Arkan-
sas, and Louisiana. Petitioner Tarrant Regional Water
District (Tarrant), a Texas agency, claims that it is enti-
tled to acquire water under the Compact from within
Oklahoma and that therefore the Compact pre-empts
several Oklahoma statutes that restrict out-of-state diver-
sions of water. In the alternative, Tarrant argues that the
Oklahoma laws are unconstitutional restrictions on inter-
state commerce. We hold that Tarrant’s claims lack merit.
I

A

The Red River (or River) begins in the Llano Estacado
Mesa on the border between New Mexico and Texas.
From this broad plain, it first runs through the Texas
Panhandle and then marks the border between Texas and
Oklahoma. It continues in an easterly direction until it
reaches the shared border with Arkansas. Once the River
2 TARRANT REGIONAL WATER DIST. v. HERRMANN

Opinion of the Court

enters Arkansas, it turns southward and flows into Loui-
siana, where it empties into the Mississippi and Atchafa-
laya Rivers.
As an important geographic feature of this region, the
Red River has lent its name to a valley, a Civil War cam-
paign, and a famed college football rivalry between the
Longhorns of Texas and the Sooners of Oklahoma. But
college pride has not been the only source of controversy
between Texas and Oklahoma regarding the Red River.
The River has been the cause of numerous historical con-
flicts between the two States, leading to a mobilization of
their militias at one time, Oklahoma v. Texas, 258 U. S.
574, 580 (1922), and the declaration of martial law along a
stretch of the River by Oklahoma Governor “Alfalfa Bill”
Murray at another, see Okla. H. Res. 1121, 50th Legisla-
ture, 2d Sess. (2006) (resolution commemorating “Alfalfa
Bill” Murray’s actions during the “Red River Bridge War”).
Such disputes over the River and its waters are a natural
result of the River’s distribution of water flows. The Riv-
er’s course means that upstream States like Oklahoma
and Texas may appropriate substantial amounts of water
from both the River and its tributaries to the disadvantage
of downstream States like Arkansas and especially Lou-
isiana, which lacks sufficiently large reservoirs to store
water.
Absent an agreement among the States, disputes over
the allocation of water are subject to equitable apportion-
ment by the courts, Arizona v. California, 460 U. S. 605,
609 (1983), which often results in protracted and costly
legal proceedings. Thus in 1955, to forestall future dis-
putes over the River and its water, Congress authorized
the States of Arkansas, Louisiana, Oklahoma, and Texas
to negotiate a compact to apportion the water of the Red
River basin among themselves. See Act of Aug. 11, 1955,
Pub. L. 346, 69 Stat. 654. These negotiations lasted over
20 years and finally culminated in the signing of the Red
 Cite as: 569 U. S. ____ (2013) 3

Opinion of the Court

River Compact in 1978. Congress approved the Compact
in 1980, transforming it into federal law. See Act of Dec.
22, 1980, 94 Stat. 3305; Compact, 1 App. 7–51.
One of the Compact’s principal purposes was “[t]o pro-
vide an equitable apportionment among the Signatory
States of the water of the Red River and its tributaries.”
§1.01(b), id., at 9. The Compact governs the allocation of
water along the Red River and its tributaries from the
New Mexico and Texas border to its terminus in Louisi-
ana. §§2.12(a)–(e), id., at 13. This stretch is divided into
five separate subdivisions called “Reach[es],” ibid., each of
which is further divided into smaller “subbasins,” see, e.g.,
§§5.01–5.05, id., at 22–26 (describing subbasins 1 through
5 of Reach II). (See Appendix A, infra, for a map.)
At issue in this case are rights under the Compact to
water located in Oklahoma’s portion of subbasin 5 of
Reach II, which occupies “that portion of the Red River,
together with its tributaries, from Denison Dam down to
the Arkansas-Louisiana state boundary, excluding all
tributaries included in the other four subbasins of Reach
II.” §5.05(a), 1 App. 24–25. (See Appendix B, infra, for a
map.) The Compact’s interpretive comments1 explain that
during negotiations, Reach II posed the greatest difficulty
to the parties’ efforts to reach agreement. Comment on
Art. V, 1 App. 27. The problem was that Louisiana, the
farthest downstream State, lacks suitable reservoir sites
and therefore cannot store water during high flow periods
to meet its future needs. The upstream States (Texas,
Oklahoma, and Arkansas), which control the River’s flow,
were unwilling to release water stored within their own
reservoirs for the benefit of any downstream States, like

——————
1 Interpretive
comments were included in the Compact so that future
readers “might be apprised of the intent of the Compact Negotiation
Committee with regard to each Article of the Compact.” Compact,
Comment on Preamble, 1 App. 9.
4 TARRANT REGIONAL WATER DIST. v. HERRMANN

Opinion of the Court

Louisiana. Without any such release, there would be no
guaranteed flow of water to Louisiana.
The provisions of the Compact relating to Reach II were
crafted to address this problem. To this end, Reach II was
divided into five subbasins. The upstream subbasins,
numbered 1 through 4, were drawn to end at “existing,
authorized or proposed last downstream major damsites,”
see, e.g., §5.01(a), id., at 22, on the tributaries leading to
the Red River before reaching the main stem of the River.
These dams allow the parties managing them to control
water along the tributaries before it travels farther down-
stream and joins the flow of the main stem of the River.
For the most part, the Compact granted control over the
water in these subbasins to the States in which each
subbasin is located.2 The remaining subbasin, subbasin 5,
instead requires that water be allowed to flow to Louisi-
ana through the main stem of the River at certain mini-
mum levels, assuring Louisiana an allocation of the River’s
waters and solving its flowthrough problem.
The provision of the Compact central to the present
dispute is §5.05(b)(1), which sets the following allocation
during times of normal flow:
“(1) The Signatory States shall have equal rights to
the use of runoff originating in subbasin 5 and un-
——————
2 Within subbasins 1, 2, and 4, water was fully apportioned to a single

State. See Compact §5.01(b), id., at 22–23 (apportioning water of
subbasin 1 and its “unrestricted use” to Oklahoma); §5.02(b), id., at 23
(same for Texas with respect to subbasin 2); §5.04(b), id., at 24 (same
for Texas with respect to subbasin 4). Only subbasin 3, which includes
portions of Oklahoma and Arkansas, breaks from this pattern and was
divided along the lines of a 60-to-40 split, with both States having “free
and unrestricted use of the water of this subbasin within their respec-
tive states, subject, however, to the limitation that Oklahoma shall
allow a quantity of water equal to the 40 percent of the total runoff
originating below the following existing, authorized or proposed last
major downstream damsites in Oklahoma to flow into Arkansas.”
§5.03(b), id., at 23–24.
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Opinion of the Court

designated water flowing into subbasin 5, so long as
the flow of the Red River at the Arkansas-Louisiana
state boundary is 3,000 cubic feet per second [herein-
after CFS] or more, provided no state is entitled to
more than 25 percent of the water in excess of 3,000
[CFS].”3 Id., at 25.
In these normal circumstances (i.e., when flows at the
Arkansas-Louisiana border are above 3,000 CFS), this
provision and its interpretive comment make clear that
“all states are free to use whatever amount of water they
can put to beneficial use.” Comment on Art. V, id., at 30.
But if the amount of water above 3,000 CFS cannot satisfy
all such uses, then “each state will honor the other’s right
to 25% of the excess flow.” Ibid. However, when the flow
of the River diminishes at the Arkansas-Louisiana border,
the upstream States must permit more water to reach
Louisiana.4 Subbasin 5’s allocation scheme allows up-
——————
3 The Compact defines “undesignated water” as “all water released
from storage other than ‘designated water.’ ” §3.01(l), id., at 17.
“[D]esignated water” means “water released from storage, paid for by
non-Federal interests, for delivery to a specific point of use or diver-
sion.” §3.01(k), ibid.
4 In such circumstances, the two relevant paragraphs provide:

“(2) Whenever the flow of the Red River at the Arkansas-Louisiana
state boundary is less than 3,000 [CFS], but more than 1,000 [CFS],
the States of Arkansas, Oklahoma, and Texas shall allow to flow into the
Red River for delivery to the State of Louisiana a quantity of water
equal to 40 percent of the total weekly runoff originating in subbasin
5 and 40 percent of undesignated water flowing into subbasin 5; pro-
vided, however, that this requirement shall not be interpreted to require
any state to release stored water.
“(3) Whenever the flow of the Red River at the Arkansas-Louisiana
state boundary falls below 1,000 [CFS], the States of Arkansas, Okla-
homa, and Texas shall allow a quantity of water equal to all the weekly
runoff originating in subbasin 5 and all undesignated water flowing in
subbasin 5 within their respective states to flow into the Red River as
required to maintain a 1,000 [CFS] flow at the Arkansas-Louisiana
state boundary.” §5.05(b), id., at 25.
6 TARRANT REGIONAL WATER DIST. v. HERRMANN

Opinion of the Court

stream States to keep the water that they have stored, but
also ensures that Louisiana will receive a steady supply of
water from the Red River, with each upstream State
contributing during times of low flow.
To ensure that its apportionments are honored, the
Compact includes an accounting provision, but an account-
ing is not mandatory “until one or more affected states
deem the accounting necessary.” §2.11, id., at 13; see
Comment on Art. II, id., at 15–16. This is because the
“extensive gaging and record keeping required” to carry
out such an accounting would impose “a significant finan-
cial burden on the involved states.” Id., at 16. Given
these costs, the signatory States did “not envisio[n] that it
w[ould] be undertaken as a routine matter.” Ibid. Indeed,
it appears that no State has ever asked for such an ac-
counting in the Compact’s history. See Brief for Respond-
ents 45; Reply Brief 11–12.
While the Compact allocates water rights among its
signatories, it also provides that it should not “be deemed
to . . . [i]nterfere with or impair the right or power of any
Signatory State to regulate within its boundaries the
appropriation, use, and control of water, or quality of
water, not inconsistent with its obligations under this
Compact.” §2.10, 1 App. 12. Rather, “[s]ubject to the
general constraints of water availability and the appor-
tionment of the Compact, each state [remains] free to
continue its existing internal water administration.”
Comment on Art. II, id., at 14. Even during periods of
water shortage, “no attempt is made to specify the steps
that will be taken [by States to ensure water deliveries]; it
is left to the state’s internal water administration.” Ibid.
B
In the years since the Red River Compact was ratified
by Congress, the region’s population has increased dra-
matically. In particular, the population of the Dallas-Fort
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Opinion of the Court

Worth metropolitan area in north Texas has grown from
roughly 5.1 million inhabitants in 2000 to almost 6.4
million in 2010, a jump of over 23 percent and among the
largest in the United States during this period. See Dept.
of Commerce, Census Bureau, P. Mackun & S. Wilson,
Population Distribution and Change: 2000 to 2010 (Mar.
2011). This growth has strained regional water supplies,
and north Texas’ need for water has been exacerbated in
recent years by a long and costly drought. See generally
Galbraith, A Drought More Than Texas-Size, International
Herald Tribune, Oct. 3, 2011, p. 4.
Against this backdrop, petitioner Tarrant, a Texas state
agency responsible for providing water to north-central
Texas (including the cities of Fort Worth, Arlington, and
Mansfield), has endeavored to secure new sources of water
for the area it serves. From 2000 to 2002, Tarrant, along
with several other Texas water districts, offered to pur-
chase water from Oklahoma and the Choctaw and Chicka-
saw Nations. See 2 App. 336–382. But these negotiations
were unsuccessful and Tarrant eventually abandoned
these efforts.
Because Texas’ need for water only continued to grow,
Tarrant settled on a new course of action. In 2007, Tar-
rant sought a water resource permit from the Oklahoma
Water Resources Board (OWRB),5 respondents here, to
take 310,000 acre feet6 per year of surface water from the
——————
5 Under §2.10 of the Compact each signatory State retains “the right
or power . . . to regulate within its boundaries the appropriation, use,
and control of water.” Id., at 12. Thus, the Compact does not expressly
pre-empt any state laws that address the control of water. Oklahoma
law, in turn, requires that any “state or federal governmental agency”
that “intend[s] to acquire the right to the beneficial use of any water” in
Oklahoma must apply to the OWRB for “a permit to appropriate” water
before “commencing any construction” or “taking [any water] from any
constructed works.” Okla. Stat., Tit. 82, §105.9 (West 2013).
6 An acre-foot is equivalent to the volume of one acre of surface area

filled to a depth of one foot. Webster’s Third New International Dic-
8 TARRANT REGIONAL WATER DIST. v. HERRMANN

Opinion of the Court

Kiamichi River, a tributary of the Red River located in
Oklahoma. Tarrant proposed to divert the Kiamichi River,
at a point located in subbasin 5 of Reach II, before it dis-
charges into the Red River and, according to Tarrant, be-
comes too saline for potable use.
Tarrant knew, however, that Oklahoma would likely
deny its permits because various state laws (collectively,
the Oklahoma water statutes) effectively prevent out-of-
state applicants from taking or diverting water from within
Oklahoma’s borders. These statutes include a require-
ment that the OWRB consider, when evaluating an appli-
cation to take water out of State, whether that water
“could feasibly be transported to alleviate water short-
ages in the State of Oklahoma.” Okla. Stat., Tit. 82,
§105.12(A)(5) (West 2013). The statutes also require that
no permit issued by the OWRB to use water outside of the
State shall “[i]mpair the ability of the State of Oklahoma
to meet its obligations under any interstate stream com-
pact.” §105.12A(B)(1). A separate provision creates a
permitting review process that applies only to out-of-
state water users. §105.12(F). Oklahoma also requires
legislative approval for out-of-state water-use permits,
§105.12A(D), and further provides that “[w]ater use within
Oklahoma . . . be developed to the maximum extent feasi-
ble for the benefit of Oklahoma so that out-of-state down-
stream users will not acquire vested rights therein to the
detriment of the citizens of this state,” §1086.1(A)(3).
Interpreting these laws, Oklahoma’s attorney general has
concluded that “we consider the proposition unrealistic
that an out-of-state user is a proper permit applicant
before the [OWRB]” because “[w]e can find no intention to
create the possibility that such a valuable resource as
water may become bound, without compensation, to use by
an out-of-state user.” 1 App. 118.
——————
tionary 19 (1966).
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Opinion of the Court

When Tarrant filed its permit application, it also filed
suit against respondents in Federal District Court. As
relevant here, Tarrant sought to enjoin enforcement of the
Oklahoma water statutes by the OWRB. Tarrant argued
that the statutes, and the interpretation of them adopted
by Oklahoma’s attorney general, were pre-empted by
federal law and violated the Commerce Clause by discrim-
inating against interstate commerce in water.
The District Court granted summary judgment for the
OWRB on both of Tarrant’s claims. See No. CIV–07–
0045–HE, 2010 WL 2817220, *4 (WD Okla., July 16,
2010); No. CIV–07–0045–HE (WD Okla., Nov. 18, 2009),
App. to Pet. for Cert. 72a–73a, 2009 WL 3922803, *8. The
Tenth Circuit affirmed. 656 F. 3d 1222, 1250 (2011).7
We granted Tarrant’s petition for a writ of certiorari,
568 U. S. ___ (2013), and now affirm the judgment of the
Tenth Circuit.
II

A

Tarrant claims that under §5.05(b)(1) of the Compact, it
has the right to cross state lines and divert water from
Oklahoma located in subbasin 5 of Reach II and that the
Oklahoma water statutes interfere with its ability to
exercise that right. Section 5.05(b)(1) provides:
“The Signatory States shall have equal rights to the
use of runoff originating in subbasin 5 and undesig-
nated water following into subbasin 5, so long as the
flow of the Red River at the Arkansas-Louisiana state
boundary is 3,000 [CFS] or more, provided no state is
entitled to more than 25 percent of the water in excess
of 3,000 [CFS].” 1 App. 25.
——————
7 The parties have stipulated that OWRB will not take action on

Tarrant’s application until this litigation has concluded. Brief for Peti-
tioner 16.
10 TARRANT REGIONAL WATER DIST. v. HERRMANN

Opinion of the Court

In Tarrant’s view, this provision essentially creates a
borderless common in which each of the four signatory
States may cross each other’s boundaries to access a
shared pool of water. Tarrant reaches this interpretation
in two steps. First, it observes that §5.05(b)(1)’s “equal
rights” language grants each State an equal entitlement to
the waters of subbasin 5, subject to a 25 percent cap.
Second, Tarrant argues §5.05(b)(1)’s silence concerning
state lines indicates that the Compact’s drafters did not
intend to allocate water according to state borders in this
section. According to Tarrant, “the ‘25 percent’ language
[of §5.05(b)(1)] makes clear that, in exercising its ‘equal
rights’ to the common pool of water, no State may take
more than a one-quarter share,” Reply Brief 3, but any of
the signatory States may “cross state lines to obtain [its]
shar[e] of Subbasin 5 waters,” Brief for Petitioner 32.
The OWRB disputes this reading. In its view, the
“equal rights” promised by §5.05(b)(1) afford each State an
equal opportunity to make use of the excess water within
subbasin 5 of Reach II but only within each State’s own
borders. This is because the OWRB reads §5.05(b)(1)’s
silence differently from Tarrant. The OWRB interprets
that provision’s absence of language granting any cross-
border rights to indicate that the Compact’s drafters had
no intention to create any such rights in the signatory
States.
Unraveling the meaning of §5.05(b)(1)’s silence with
respect to state lines is the key to resolving whether the
Compact pre-empts the Oklahoma water statutes.8 If
——————
8 The Compact Clause of the Constitution provides that “[n]o State

shall, without the Consent of Congress, . . . enter into any Agreement or
Compact with another State.” Art. I, §10, cl. 3. Accordingly, before a
compact between two States can be given effect it must be approved by
Congress. See Virginia v. Maryland, 540 U. S. 56, 66 (2003). Once a
compact receives such approval, it is “transform[ed] . . . into a law of
the United States.” Ibid. (internal quotation marks omitted). The
 Cite as: 569 U. S. ____ (2013) 11

Opinion of the Court

§5.05(b)(1)’s silence means that state borders are irrele-
vant to the allocation of water in subbasin 5 of Reach II,
then the Oklahoma water laws at issue conflict with the
cross-border rights created by federal law in the form of
the Compact and must be pre-empted. But if §5.05(b)(1)’s
silence instead reflects a background understanding on
the part of the Compact’s drafters that state borders were
to be respected within the Compact’s allocation, then the
Oklahoma statutes do not conflict with the Compact’s
allocation of water.
B
Interstate compacts are construed as contracts under
the principles of contract law. Texas v. New Mexico, 482
U. S. 124, 128 (1987). So, as with any contract, we begin
by examining the express terms of the Compact as the
best indication of the intent of the parties, see also Mon-
tana v. Wyoming, 563 U. S. ___, ___, and n. 4, ___, (2011)
(slip op., at 5, and n. 4, 17); Restatement (Second) of Con-
tracts §203(b) (1979).
Tarrant argues that because other provisions of the
Compact reference state borders, §5.05(b)(1)’s silence with
respect to state lines must mean that the Compact’s draft-
ers intended to permit cross-border diversions. For exam-
ple, §5.03(b), which governs subbasin 3 of Reach II,
provides that
“[t]he States of Oklahoma and Arkansas shall have
free and unrestricted use of the water of this subbasin
within their respective states, subject, however, to the
limitation that Oklahoma shall allow a quantity of
water equal to . . . 40 percent of the total runoff origi-

——————
Supremacy Clause, Art. VI, cl. 2, then ensures that a congressionally
approved compact, as a federal law, pre-empts any state law that
conflicts with the Compact. See Fidelity Fed. Sav. & Loan Assn. v. De
la Cuesta, 458 U. S. 141, 152–153 (1982).
12 TARRANT REGIONAL WATER DIST. v. HERRMANN

Opinion of the Court

nating below the following existing, authorized or
proposed last major downstream damsites in Okla-
homa to flow into Arkansas.” 1 App. 23–24 (emphasis
added).
Section 6.03(b), which covers subbasin 3 of Reach III,
similarly provides that “Texas and Louisiana within their
respective boundaries shall each have the unrestricted use
of the water of this subbasin subject to the following
[conditions].” Id., at 33 (emphasis added). Thus, §5.03(b)
and §6.03(b) mimic §5.05(b)(1) in allocating water rights
within a subbasin, but differ in that they make explicit ref-
erence to water use “within” state boundaries. Relying on
the expressio unius canon of construction, Tarrant finds
that §5.05(b)’s silence regarding borders is significant
because “ ‘[w]here Congress includes particular language
in one section of a statute but omits it in another section of
the same Act, it is generally presumed [that] Congress
acts intentionally and purposely in the disparate inclusion
or exclusion.’ ” Brief for Petitioner 29 (quoting Russello v.
United States, 464 U. S. 16, 23 (1983)).
But Tarrant’s argument fails to account for other sec-
tions of the Compact that cut against its reading. For
example, §5.05(b)(3), which governs the waters of subbasin
5 in Reach II when flows are below 1,000 CFS, requires
that during such periods, Arkansas, Texas, and Oklahoma
allow water “within their respective states to flow into the
Red River as required to maintain a 1,000 [CFS] flow at
the Arkansas-Louisiana state boundary.” 1 App. 25 (em-
phasis added). Obviously none of the upstream States can
redirect water that lies outside of their borders, so the
phrase “within their respective states” is superfluous in
§5.05(b)(3). In contrast, §5.05(b)(2), which governs when
the River’s flow at the Arkansas-Louisiana border is above
1,000 CFS but below 3,000 CFS, requires that upstream
States allow a flow to Louisiana equivalent to 40 percent
 Cite as: 569 U. S. ____ (2013) 13

Opinion of the Court

of total weekly runoff originating within the subbasin and
40 percent of undesignated water flowing into subbasin 5
of Reach II. Id., at 25. This language can only refer to
water within each State’s borders because otherwise each
State would have to contribute 40 percent to the total
water flow, which would add up to more than 100 percent.
Read together and to avoid absurd results, §§5.05(b)(2)
and (3) suggest that each upstream State is individually
responsible for ensuring that sufficient subbasin 5 water
located within its respective borders flows down to Louisi-
ana, even though §5.05(b)(2) lacks any explicit reference to
state lines.
Applying Tarrant’s understanding of §5.05(b)(1)’s si-
lence regarding state lines to other of the Compact’s provi-
sions would produce further anomalous results. Consider
§6.01(b). That provision states that “Texas is apportioned
sixty (60) percent of the runoff of [subbasin 1 of Reach III]
and shall have unrestricted use thereof; Arkansas is enti-
tled to forty (40) percent of the runoff of this subbasin.”
Id., at 32. Because Texas is upstream from Arkansas,
water flows from Texas to Arkansas. Given this situation,
the commonsense reason for §6.01(b)’s 60-to-40 allocation
is to prevent Texas from barring the flow of water to Ar-
kansas. While there is no reference to state boundaries in
the section’s text, the unstated assumption underlying this
provision is that Arkansas must wait for its 40 percent
share to go through Texas before it can claim it. But
applying Tarrant’s understanding of silence regarding
state borders to this section would imply that Arkansas
could enter into Texas without having to wait for the
water that will inevitably reach it. This counterintuitive
outcome would thwart the self-evident purposes of the
Compact. Further, other provisions of the Compact share
this structure of allocating a proportion of water that will
14 TARRANT REGIONAL WATER DIST. v. HERRMANN

Opinion of the Court

flow from an upstream State to a downstream one.9 Ac-
cepting Tarrant’s reading would upset the balance struck
by all these sections.
At the very least, the problems that arise from Tarrant’s
proposed reading suggest that §5.05(b)(1)’s silence is
ambiguous regarding cross-border rights under the Com-
pact. We therefore turn to other interpretive tools to shed
light on the intent of the Compact’s drafters. See Okla-
homa v. New Mexico, 501 U. S. 221, 235, n. 5 (1991).10
Three things persuade us that cross-border rights were
not granted by the Compact: the well-established principle
that States do not easily cede their sovereign powers,
including their control over waters within their own terri-
tories; the fact that other interstate water compacts have
treated cross-border rights explicitly; and the parties’
course of dealing.
1
The background notion that a State does not easily cede
its sovereignty has informed our interpretation of inter-
state compacts. We have long understood that as sover-
eign entities in our federal system, the States possess an
——————
9 See Compact §4.01(b), 1 App. 18 (“The annual flow within this sub-

basin is hereby apportioned sixty (60) percent to Texas and forty (40)
percent to Oklahoma”); §6.02(b), id., at 32 (“Arkansas is apportioned
sixty (60) percent of the runoff of this subbasin and shall have unre-
stricted use thereof; Louisiana is entitled to forty (40) percent of the
runoff of this subbasin”).
10 There is, however, one interpretive tool that is inapplicable here:

the presumption against pre-emption. The Court of Appeals repeatedly
referenced and relied upon the presumption in its opinion. See 656
F. 3d 1222, 1239, 1242, 1245–1246 (CA10 2011). Yet the presumption
against pre-emption is rooted in “respect for the States as ‘independent
sovereigns in our federal system’ ” and “assume[s] that ‘Congress does
not cavalierly pre-empt’ ” state laws. Wyeth v. Levine, 555 U. S. 555,
565–566, n. 3 (2009). When the States themselves have drafted and
agreed to the terms of a compact, and Congress’ role is limited to
approving that compact, there is no reason to invoke the presumption.
 Cite as: 569 U. S. ____ (2013) 15

Opinion of the Court

“absolute right to all their navigable waters and the soils
under them for their own common use.” Martin v. Lessee
of Waddell, 16 Pet. 367, 410 (1842). Drawing on this
principle, we have held that ownership of submerged
lands, and the accompanying power to control navigation,
fishing, and other public uses of water, “is an essen-
tial attribute of sovereignty,” United States v. Alaska,
521 U. S. 1, 5 (1997). Consequently, “ ‘[a] court deciding
a question of title to [a] bed of navigable water [within a
State’s boundaries] must . . . begin with a strong presump-
tion’ against defeat of a State’s title.” Id., at 34 (quoting
Montana v. United States, 450 U. S. 544, 552 (1981)). See
also Solid Waste Agency of Northern Cook Cty. v. Army
Corps of Engineers, 531 U. S. 159, 174 (2001); Utah Div. of
State Lands v. United States, 482 U. S. 193, 195 (1987).
Given these principles, when confronted with silence in
compacts touching on the States’ authority to control their
waters, we have concluded that “[i]f any inference at all is
to be drawn from [such] silence on the subject of regula-
tory authority, we think it is that each State was left to
regulate the activities of her own citizens.” Virginia v.
Maryland, 540 U. S. 56, 67 (2003). Cf. New Jersey v. New
York, 523 U. S. 767, 783, n. 6 (1998) (“[T]he silence of
the Compact was on the subject of settled law governing
avulsion, which the parties’ silence showed no intent to
modify”).
Tarrant asks us to infer from §5.05(b)(1)’s silence re-
garding state borders that the signatory States have
dispensed with the core state prerogative to control water
within their own boundaries.11 But as the above demon-
——————
11 Of course, the power of States to control water within their borders

may be subject to limits in certain circumstances. For example, those
imposed by the Commerce Clause. See Sporhase v. Nebraska ex rel.
Douglas, 458 U. S. 941, 954–958 (1982). Here we deal only with
whether the parties’ silence on state boundaries in the allocation of
water under a compact suggests that borders are irrelevant for that
16 TARRANT REGIONAL WATER DIST. v. HERRMANN

Opinion of the Court

strates, States rarely relinquish their sovereign powers, so
when they do we would expect a clear indication of such
devolution, not inscrutable silence. We think that the
better understanding of §5.05(b)(1)’s silence is that the
parties drafted the Compact with this legal background in
mind, and therefore did not intend to grant each other
cross-border rights under the Compact.
In response, Tarrant contends that its interpretation
would not intrude on any sovereign prerogative of Okla-
homa because that State would retain its authority to
regulate the water within its borders. Because anyone
seeking water from Oklahoma would still have to apply to
the OWRB, receive a permit, and abide by its conditions,
Tarrant argues that Oklahoma’s sovereign authority
remains untouched by its interpretation. But Tarrant
cannot have it both ways. Adopting Tarrant’s reading
would necessarily entail assuming that Oklahoma and
three other States silently surrendered substantial control
over the water within their borders when they agreed to
the Compact. Given the background principles we have
described above, we find this unlikely to have been the
intent of the Compact’s signatories.
2
Looking to the customary practices employed in other
interstate compacts also helps us to ascertain the intent of
the parties to this Compact. See Alabama v. North Carolina,
560 U. S. 330 ___, ___ (2010) (slip op., at 9); Oklahoma,
501 U. S., at 235, n. 5; Texas v. New Mexico, 462 U. S.
554, 565 (1983). See also Restatement (Second) of Con-
tracts §203(b) (explaining that “usage of trade” may be
relevant in interpreting a contract). Many of these other
compacts feature language that unambiguously permits
——————
allocation. As noted infra, at 23–24, Tarrant has not raised any Com-
merce Clause challenge to Oklahoma’s control of the water allocated to
it by the Compact.
 Cite as: 569 U. S. ____ (2013) 17

Opinion of the Court

signatory States to cross each other’s borders to fulfill
obligations under the compacts. See, e.g., Amended Bear
River Compact, Art. VIII(A), 94 Stat. 12 (“[N]o State shall
deny the right of another signatory State . . . to acquire
rights to the use of water . . . in one State for use of water
in another”).12 The absence of comparable language in the
Red River Compact counts heavily against Tarrant’s read-
ing of it.
Tellingly, many of these compacts provide for the terms
and mechanics of how such cross-border relationships will
operate, including who can assert such cross-border rights,
see, e.g., Kansas-Nebraska Big Blue River Compact, Art.
VII(1), 86 Stat. 198, who should bear the costs of any
cross-border diversions, see, e.g., Belle Fourche River
Compact, Art. VI, 58 Stat. 96–97, and how such diversions
should be administered, Arkansas River Basin Compact,
Kansas-Oklahoma, Art. VII(A), 80 Stat. 1411. See also
Brief for Professors of Law and Political Science as Amici
Curiae 11–14 (giving more examples).
Provisions like these are critical for managing the com-
plexities that ensue from cross-border diversions. Consider
the mechanics of a cross-border diversion or taking of
water in this case. If Tarrant were correct, then appli-
——————
12 See also Amended Costilla Creek Compact, Art. III(2), 77 Stat. 353
(“Each State grants for the benefit of the other . . . the rights . . . in one
State for use in the other”); Klamath River Basin Compact, Art. V(A),
71 Stat. 500 (“Each state hereby grants for the benefit of the other . . .
the right . . . in one state for use in the other”); Snake River Compact,
Art. VIII(A), 64 Stat. 32 (“[N]either State shall deny the right of the
other State to acquire rights to the use of water . . . in one State for use
in the other”); South Platte River Compact, Art. VI(1), 44 Stat. 198
(“Colorado consents that Nebraska and its citizens may . . . divert water
from the South Platte River within Colorado for use in Nebraska”);
Upper Colorado River Basin Compact, Art. IX(a), 63 Stat. 37 (“[N]o
State shall deny the right of another signatory State . . . to acquire
rights to the use of water . . . in an upper signatory State for consump-
tive use in a lower signatory State”).
18 TARRANT REGIONAL WATER DIST. v. HERRMANN

Opinion of the Court

cants from Arkansas, Texas, and Louisiana could all apply
to the OWRB for permits to take water from Oklahoma.
The OWRB would then be obligated to determine the total
amount of water in Oklahoma beyond the 25 percent cap
created in §5.05(b)(1), given that the Compact would only
obligate Oklahoma to deliver water beyond its quarter
share. This alone would be a herculean task because the
Compact does not require ongoing monitoring or account-
ing, see Compact §2.11, 1 App. 13, and not all of the water
in subbasin 5 is located or originates in Oklahoma. More-
over, the OWRB would be tasked with determining the
priority under the Compact of applicants from other
States. This would almost certainly require the OWRB to
not only determine whether Oklahoma had received more
or less than its 25 percent allotment, but whether other
States had as well. Put plainly, the end result would be
a jurisdictional and administrative quagmire. The pro-
visions in the other interstate water compacts resolve
these complications. The absence of comparable provisions
in the Red River Compact strongly suggests that cross-
border rights were never intended to be part of the States’
agreement.
Tarrant counters that not all interstate compacts that
permit cross-border diversions have explicit language to
this effect. On this front, Tarrant manages to identify one
interstate compact that it contends permits cross-border
diversions without express language to that effect, the
Upper Niobrara River Compact, Pub. L. 91–52, 83 Stat.
86. Tarrant observes that this compact, which deals with
a river mostly located in Nebraska with only a small
portion in Wyoming, provides that “[t]here shall be no
restrictions on the use of the surface waters of [the river]
by Wyoming.” See Art. V(A)1, id., at 88. Tarrant suggests
that this language, coupled with the fact that the bulk of
the river is in Nebraska, implicitly indicates that the
compact grants Wyoming a right to enter Nebraska and
 Cite as: 569 U. S. ____ (2013) 19

Opinion of the Court

use the river’s water. First, we are not convinced that a
single compact’s failure to reference state borders does
much to detract from the overall custom in this area. See
supra, at 16–18, and n. 12. Second, the Upper Niobrara
River Compact is not a helpful counterexample for Tar-
rant. The general provision that Tarrant quotes is paired
with a host of detailed conditions. See Arts. V(A)1(a)–(f),
83 Stat. 88. Contrary to Tarrant’s position, then, assum-
ing that the Upper Niobrara River compact does create
any cross-border rights, it does so not through silence, but
through the detailed scheme that would apply to any such
contemplated diversions.
Tarrant also argues that §2.05(d) of the Red River Com-
pact, which provides that “[e]ach Signatory State shall
have the right to” “[u]se the bed and banks of the Red
River and its tributaries to convey stored water, imported
or exported water, and water apportioned according to this
Compact,” 1 App. 11, in fact authorizes cross-border diver-
sions. Because the present border between Texas and
Oklahoma east of the Texas Panhandle is set by the vege-
tation line on the south bank of the River, Red River
Boundary Compact, 114 Stat. 919, Tarrant contends that
§2.05(d) reflects an understanding on the part of the Com-
pact’s drafters that state borders could be crossed. But the
issue is not as simple as Tarrant makes it out to be. When
the Compact was drafted, the Texas-Oklahoma border was
fixed at the south bank of the River. See Texas v. Okla-
homa, 457 U. S. 172 (1982). If Texas was able to access
water through the south bank of the River—an issue left
unbriefed by the parties—the Compact’s framers may
have believed that Texas could reach the River and take
water from it without having to enter Oklahoman land,
casting doubt on Tarrant’s theory. In any event, even if
§2.05(d) is read to establish a cross-border right, it does so
through express language setting forth the location and
purposes under which such an incursion is permissible.
20 TARRANT REGIONAL WATER DIST. v. HERRMANN

Opinion of the Court

This is different from the inference from silence that
Tarrant asks us to draw in §5.05(b)(1).
3
The parties’ conduct under the Compact also under-
mines Tarrant’s position. A “part[y’s] course of perfor-
mance under the Compact is highly significant” evidence
of its understanding of the compact’s terms. Alabama v.
North Carolina, 560 U. S., at___ (slip op., at 14). Since the
Compact was approved by Congress in 1980, no signatory
State had pressed for a cross-border diversion under the
Compact until Tarrant filed its suit in 2007. Brief for
Respondents 26, 49–51. Indeed, Tarrant attempted to
purchase water from Oklahoma over the course of 2000
until 2002, see supra, at 7, a strange offer if Tarrant be-
lieved it was entitled to demand such water without pay-
ment under the Compact.
In response, Tarrant maintains that there were “compel-
ling business reasons” for it to purchase water. Reply
Brief 17. We are unpersuaded. If Tarrant believed that it
had a right to water located in Oklahoma, there would
have been “compelling business reasons” to mention this
right given that billions of dollars were at stake. See 2
App. 362–363 (summarizing Texas purchase proposal).
Yet there is no indication that Tarrant or any other Texas
agency or the State of Texas itself previously made any
mention of cross-border rights within the Compact, and
none of the other signatory States has ever made such a
claim.
4
The Compact creates no cross-border rights in Texas.
Tarrant’s remaining arguments do not persuade us
otherwise.
First, Tarrant argues that its interpretation of the
Compact is necessary to realize the “structure and purpose
 Cite as: 569 U. S. ____ (2013) 21

Opinion of the Court

of Reach II.” Brief for Petitioner 34–38. Tarrant contends
that because the boundary of subbasin 5 is set by the
location of the last existing, authorized, or proposed sites
for a downstream dam before the Red River, see Compact
§§5.01(a), 5.02(a), 5.03(b), 5.04(a), 1 App. 22–24, the Com-
pact allows each of the States upstream from Louisiana to
prevent water from flowing from its tributaries into sub-
basin 5. Tarrant reasons that each State will therefore
hold whatever water it needs in its upstream basins.
Given this, Tarrant maintains that any water that a State
voluntarily allows to reach subbasin 5 must be surplus
water that State did not intend to use, and if the upstream
State has no need for that water, then there is no reason
not to allow other States to access and use it, even across
borders.
This argument is founded on a shaky premise: It as-
sumes that flows from these dammed-up tributaries are
the sole source of water in subbasin 5. But §5.05(b)(1)
explains that “[s]ignatory States shall have equal rights to
the use of runoff originating in subbasin 5,” as well as
“water flowing into subbasin 5,” which would include flows
from the main stem of the River itself. Id., at 25. Thus,
there are waters that are specific to subbasin 5 separate
from those originating in the tributaries covered by sub-
basins 1 through 4. Tarrant’s account of the purposes of
subbasin 5 does not explain how these waters were to be
allocated.
Tarrant’s second argument regarding the purposes of
Reach II is that §5.05(b)(1)’s 25 percent cap on each State’s
access to excess water in subbasin 5 should be read to
imply that if a State cannot access sufficient water within
its borders to meet its share under the cap, then it must be
able to cross borders to reach that water. Were it other-
wise, Tarrant explains, the 25 percent cap would have no
purpose. To support this argument, Tarrant draws on a
1970 engineering report that it contends shows that only
22 TARRANT REGIONAL WATER DIST. v. HERRMANN

Opinion of the Court

16 percent of the freshwater flowing into subbasin 5 was
located in Texas. Brief for Petitioner 9, n. 5. The OWRB
challenges this percentage with its own calculations
drawn from the report, and asserts that Texas had access
to at least 29 percent of the excess water in subbasin 5
within its own borders. Brief for Respondents 26, 47–48,
and n. 17.
Fortunately, we need not delve into calculations based
on a decades-old engineering report to resolve this argu-
ment. As we have explained, supra, at 4–6, Texas does not
have a minimum guarantee of 25 percent of the excess
water in subbasin 5. If it believes that Oklahoma is using
more than its 25 percent allotment and wishes to stop it
from doing so, then it may call for an accounting under
§2.11 of the Compact and, depending on the results of that
accounting, insist that Oklahoma desist from taking more
than its provided share. See Compact §2.11, and Com-
ment on Art. II, 1 App. 13–16. This is the appropriate
remedy provided under the Compact. But Texas has never
done so and Tarrant offers no evidence that in the present
day Texas cannot access its 25 percent share on its own
land.
C
Under the Compact’s terms, water located within Okla-
homa’s portion of subbasin 5 of Reach II remains under
Oklahoma’s control. Accordingly, Tarrant’s theory that
Oklahoma’s water statutes are pre-empted because they
prevent Texas from exercising its rights under the Com-
pact must fail for the reason that the Compact does not
create any cross-border rights in signatory States.
III
Tarrant also challenges the constitutionality of the
Oklahoma water statutes under a dormant Commerce
Clause theory. Tarrant argues that the Oklahoma water
 Cite as: 569 U. S. ____ (2013) 23

Opinion of the Court

statutes impermissibly “ ‘discriminat[e] against interstate
commerce’ for the ‘forbidden purpose’ of favoring local
interests” by erecting barriers to the distribution of water
left unallocated under the Compact. Brief for Petitioner
47–48 (quoting Department of Revenue of Ky. v. Davis, 553
U. S. 328, 338 (2008)). Tarrant’s argument is premised on
the position that if we “adopt the Tenth Circuit’s or re-
spondent’s interpretation [of the Compact], . . . a substan-
tial amount of Reach II, Subbasin 5 water located in Ok-
lahoma is not apportioned to any State and therefore is
available to permit applicants like Tarrant.” Brief for
Petitioner 47. So, Tarrant continues, because Oklahoma’s
laws prevent this “unallocated water” from being distrib-
uted out of State, those laws violate the Commerce Clause.
Tarrant’s assumption that that the Compact leaves
some water “unallocated” is incorrect. The interpretive
comment for Article V of the Compact makes clear that
when the River’s flow is above 3,000 CFS, “all states are
free to use whatever amount of water they can put to
beneficial use,” subject to the requirement that “[i]f the
states have competing uses and the amount of water
available in excess of 3000 CFS cannot satisfy all such
uses, each state will honor the other’s right to 25% of the
excess flow.” 1 App. 29–30. If more than 25 percent of
subbasin 5’s water is located in Oklahoma, that water is
not “unallocated”; rather, it is allocated to Oklahoma
unless and until another State calls for an accounting
and Oklahoma is asked to refrain from utilizing more than
its entitled share.13 The Oklahoma water statutes can-
not discriminate against interstate commerce with re-
spect to unallocated waters because the Compact leaves no
——————
13 Moreover, even if Oklahoma utilized less than 25 percent of the

excess subbasin 5 water within its territory and allowed the rest to flow
down the River, that water would pass from Reach II into Reach V, see
Compact §2.12, 1 App. 13, the waters of which are completely allocated
to Louisiana, §8.01, id., at 38. Again, no water is left “unallocated.”
24 TARRANT REGIONAL WATER DIST. v. HERRMANN

Opinion of the Court

waters unallocated. Tarrant’s Commerce Clause argu-
ment founders on this point.
* * *
The Red River Compact does not pre-empt Okla-
homa’s water statutes because the Compact creates no
cross-border rights in its signatories for these statutes to
infringe. Nor do Oklahoma’s laws run afoul of the Com-
merce Clause. We affirm the judgment of the Court of
Appeals for the Tenth Circuit.
It is so ordered.