delivered the opinion of the Court.
The narrow issue presented by these cases is which of two federal statutes provides the formula for distribution of revenues received from oil and gas leases on national wildlife refuges reserved from public lands.
I
The Kenai National Moose Range was created in 1941 by the withdrawal of nearly two million acres from public lands on the Kenai Peninsula in Alaska. See Exec. Order No. 8979, 3 CFR 1043 (1938-1943 Comp.). See also Public Land Order No. 3400, 29 Fed. Reg. 7094-7095 (1964) (adjusting the boundaries). The Kenai Moose Range, as its name suggests, provides a refuge and breeding ground for moose. The Fish and Wildlife Service in the Department of the Interior administers it as part of the national wildlife refuge system.
*261Commercially significant quantities of oil underlie the Kenai Moose Range.1 Pursuant to authority under the Mineral Leasing Act of 1920, 30 U. S. C. § 181 et seq., the Secretary of the Interior issued oil and gas leases for the Kenai Moose Range, beginning in the mid-1950’s. See Udall v. Tallman, 380 U. S. 1 (1965). The United States has received substantial revenues from these leases.2 From first receipt in 1954, the Secretary has distributed these revenues according to the formula provided in § 35 of the Mineral Leasing Act of 1920, 41 Stat. 450, as amended, 30 U. S. C. § 191. This formula prescribes that 90% of the revenues be paid to the State of Alaska and 10% to the United States Treasury.3
*262In 1975, the Director of the Fish and Wildlife Service inquired of the Solicitor of the Department of the Interior whether revenues from oil and gas leases in wildlife refuges created by withdrawal of public lands should be distributed according to § 401 (c) of the Wildlife Refuge Revenue Sharing Act, 49 Stat. 383, as amended, 16 U. S. C. § 715s (c), rather than under the Mineral Leasing Act of 1920. The Director’s inquiry was prompted by the 1964 amendments to § 401 (a), which added the word “minerals” to a list of refuge resources, the revenues from which were to be distributed according to the statutory formula.4 Pub. L. 88-523, 78 Stat. 701. According to this formula, 25% of the revenues are paid to counties wherein the refuge lies, and remaining funds are used by the Department of the Interior for public purposes.5 *263The Solicitor ruled that the 1964 amendment governed, superseding § 35 of the Mineral Leasing Act of 1920. App. to Pet. for Cert, in No. 79-1890, p. 26a. The Comptroller General concurred in the view of the Solicitor. 55 Comp. Gen. 117 (1975). Upon request for reconsideration by the State of Alaska in 1976, the Comptroller General affirmed his initial decision. See Op. Comp. Gen. in File: B-l 18678, June 11, 1976, reprinted in App. to Pet. for Cert, in No. 79-1890, p. 42a.
The Kenai Peninsula Borough then brought suit against the Secretary of the Interior in the United States District Court for the District of Alaska, seeking a declaration that the amended § 401 (a) of the Wildlife Refuge Revenue Sharing Act governed the distribution of oil and gas revenues from the Kenai Moose Range. Kenai Borough is the “county” within which the Moose Range lies. If § 401 (a) governs, it will receive 25% of the revenues and the State none. The State of Alaska then filed suit in the same court against the Secretary and various federal officials, seeking a declaration that § 35 of the Mineral Leasing Act still governed distribution of these same oil and gas revenues. If that provision applies, the State will continue to receive 90% of the funds and, so far as federal law is concerned, Kenai Borough none. The District Court consolidated the lawsuits.6
The District Court granted summary judgment for the State of Alaska. 436 F. Supp. 288 (1977). Upon exami*264nation of the apparently conflicting statutes, the court held that the term “minerals” in the amended Wildlife Refuge Revenue Sharing Act referred only to oil and gas found on land acquired for wildlife refuges. Id., at 292. Distribution of oil and gas revenues from leases on public land reserved for wildlife refuges, it held, continues to be determined by § 35 of the Mineral Leasing Act of 1920.7 Ibid. The court viewed the legislative history of the 1964 amendments as demonstrating that Congress was concerned primarily with the difficulties of acquiring land for refuges and that Congress expected no increase in revenues from the Kenai Moose Range to result from the amendments. Id., at 291-292.
The Court of Appeals for the Ninth Circuit affirmed. 612 F. 2d 1210 (1980). That court found the legislative history largely ambiguous. Id., at 1213. It refused to find that the addition of the word “minerals” to the amended Wildlife Refuge Revenue Sharing Act had repealed by implication the Mineral Leasing Act of 1920 without a clear showing that this was the intent of Congress. See Morton v. Mancari, 417 U. S. 535, 549-551 (1974). The court further approved the District Court’s holding because it gave effect to each statute. 612 F. 2d, at 1214-1215.
We granted certiorari. Sub nom. Andrus v. Alaska, 449 U. S. 818 (1980).8 We now affirm.
*265II
The Secretary and the Kenai Borough rely primarily on the “plain language” of § 401 (a) of the Wildlife Refuge Revenue Sharing Act. They contend that it provides without ambiguity that mineral resources from all national wildlife refuges be distributed according to the formula described in § 401 (a) of the Act. As currently phrased, § 401 (a) provides:
“[A] 11 revenues received by the Secretary of the Interior from the sale or other disposition of animals, salmonoid carcassas [sic], timber, hay, grass, or other products of the soil, minerals, shells, sand, or gravel, [or] from other privileges . . . shall be . . . reserved in a separate fund for disposition as hereafter prescribed.” 16 U. S. C. § 715s (a) (1976 ed., Supp. III).
The provision defines the wildlife refuge system to include lands “acquired or reserved” for conservation and protection of certain fish and wildlife. No restriction is placed upon the common meaning of “minerals.” Given this clarity, it is argued, resort to the legislative history is unnecessary or improper.
We agree with the Secretary that “[t]he starting point in every case involving construction of a statute is the language itself.” Blue Chip Stamps v. Manor Drug Stores, 421 U. S. *266723, 756 (1975) (Powell, J., concurring). See Rubin v. United States, 449 U. S. 424 (1981). But ascertainment of the meaning apparent on the face of a single statute need not end the inquiry. Train v. Colorado Public Interest Research Group, 426 U. S. 1, 10 (1976); United States v. American Trucking Assns., Inc., 310 U. S. 534, 543-544 (1940). This is because the plain-meaning rule is “rather an axiom of experience than a rule of law, and does not preclude consideration of persuasive evidence if it exists.” Boston Sand Co. v. United States, 278 U. S. 41, 48 (1928) (Holmes, J.).9 The circumstances of the enactment of particular legislation may persuade a court that Congress did not intend words of common meaning to have their literal effect. E. g., Church of the Holy Trinity v. United States, 143 U. S. 457, 459 (1892) ; United States v. Ryan, 284 U. S. 167, 175 (1931).
Sole reliance on the “plain language” of § 401 (a) would assume the answer to the question at issue. These cases involve two statutes, each of which by its literal terms applies to the facts before us. Restatement of the terms of § 401 (a) cannot answer which statute Congress intended to control. Recognizing this, the Secretary invokes the maxim of construction that the more recent of two irreconcilably conflicting statutes governs. 2A C. Sands, Sutherland on Statutes and Statutory Construction § 51.02 (4th ed. 1973). Without depreciating this general rule, we decline to read the statutes as being in irreconcilable conflict without seeking to ascertain the actual intent of Congress. Our examination of the *267legislative history is guided by another maxim: “ ‘repeals by implication are not favored/ ” Morton v. Mancari, 417 U. S., at 549, quoting Posadas v. National City Bank, 296 U. S. 497, 503 (1936). “The intention of the legislature to repeal must be ‘clear' and manifest.’ ” United States v. Borden Co., 308 U. S. 188, 198 (1939), quoting Red Rock v. Henry, 106 U. S. 596, 602 (1883). We must read the statutes to give'effect to each if we can do so while preserving their sense and purpose. Mancari, supra, at 551; see Haggar Co. v. Helvering, 308 U. S. 389, 394 (1940).
Ill
Congress gave extensive consideration to the purpose and probable effect of the 1964 amendments to the Wildlife Refuge Revenue Sharing Act. Pub; L. 88-523, 78 Stat. 701. Nonetheless, and we think it significant, there is no explanation in the legislative history for the addition of the single word “minerals” to the list of refuge resources subject to the Act. See H. R. Rep. No. 1753, 88th Cong., 2d Sess. (1964) (hereinafter 1964 H. R. Rep.); S. Rep. No. 1096, 88th Cong., 2d Sess. (1964) (hereinafter 1964 S. Rep.); 110 Cong. Rec. 19882-19883 (1964) (remarks of Rep. Ostertag). Our study of the few legislative materials pertinent to the insertion of “minerals” persuades us that Congress intended to work no change in the pre-existing formula for distribution of mineral revenues from federal wildlife refuges.
A
Prior to 1964, § 35 of the Mineral Leasing Act of 1920 governed distribution of revenues from mineral leases on wildlife refuges withdrawn from public lands. This conclusion cannot be seriously questioned. First, from the time the first mineral revenues were generated on such lands until well after 1964, the Secretary invariably distributed the revenues as provided in the Mineral Leasing Act. Second, the Comptroller General long ago ruled that the only other arguably *268applicable statute, the then unamended Wildlife Refuge Revenue Sharing Act, Act of June 15, 1935, ch. 261, 49 Stat. 383 (hereinafter 1935 Refuge Act), see n. 4, supra, did not govern the disposal of revenues from mineral leases on wildlife refuges. 21 Comp. Gen. 873 (1942). See also Comp. Gen., B-105133, Oct. 10, 1951, App. 82.10
Third, our opinion in Udall v. Tallman, 380 U. S. 1 (1965), strongly suggests that the Mineral Leasing Act of 1920 governed the distribution of revenues from reserved refuge lands prior to 1964. That case, involved the authority of the Secretary to issue oil leases on the Kenai Moose Range after the lands had been withdrawn from the public domain by *269Executive Order. In holding that the Executive Order did not deprive the Secretary of this power, this Court held that the Mineral Leasing Act of 1920 conferred the necessary statutory authorization on the Secretary to grant the leases. “The Act excluded from its application certain designated lands, but did not exclude land within wildlife refuge areas.” Id., at 4 (footnote omitted).11 Because §35 of the Mineral Leasing Act prescribes the distribution formula for revenues received from all leases issued “under the provisions of this chapter,” we think it an inescapable deduction from Tallman that, prior to 1964, the Act continued to provide the formula for disposition of revenues generated by leases on public lands after the lands were withdrawn for wildlife refuges.
Neither the Mineral Leasing Act of 1920 nor the 1935 Refuge Act authorized the Secretary to issue leases for mineral extraction from refuges created from acquired lands. 40 Op. Atty. Gen. 9 (1941) (Attorney General Jackson); 21 Comp. Gen. 873 (1942). Congress responded by passing the Mineral Leasing Act for Acquired Lands, Act of Aug. 7, 1947, ch. 513, 61 Stat. 913, 30 U. S. C. § 351 et seg. See n. 10, supra. In addition to conferring authority on the Secretary to issue leases for specified minerals, including oil and gas, it provided that revenues from the leases be “distributed in the same manner as prescribed for other receipts from the lands affected by the lease.” 30 U. S. C. § 355.. As' applied to wildlife refuges created from acquired lands, this provision requires that mineral revenues be distributed according to the formula in the 1935 Refuge Act.
*270Thus, when Congress amended the Wildlife Refuge Revenue Sharing Act in 1964, the disposition of oil and gas revenues was reasonably clear. Such revenues from reserved refuge lands were distributed according to the Mineral Leasing Act of 1920. Revenues from acquired refuge lands were distributed according to the formula in the 1935 Refuge Act, not by its own terms, but by operation of the 1947 Mineral Leasing Act for Acquired Lands.
B
The question presented by these cases is whether Congress intended to alter this program of revenue distribution when it amended the 1935 Refuge Act in 1964. The impetus for proposals leading to the passage of the amendments was the difficulty the Department had experienced in acquiring new refuge lands. See 1964 S. Rep. 5; 1964 H. R. Rep. 2. Localities resisted having land removed from local tax roles. The purpose of the amendments was to “provide a more equitable formula for payments to counties as compensation for loss of taxable properties that have been acquired by the Federal wildlife refuge system.” 1964 S. Rep. 2. See 1964 H. R. Rep. 2-3. Public Law 88-523 met this problem by changing the formula for distribution of revenues from refuges consisting of acquired lands. §401 (c)(1), 78 Stat. 701. The new formula provided that counties within which acquired refuge lands lay could receive, at their option, a payment based on the adjusted cost of the lands rather than on revenues produced.12 Congress intended the Department to pay more to counties under the new law than it had under the old.
There is no explanation in the legislative history of Pub. L. 88-523 for the insertion of “minerals” in the list of resources *271subject to the Wildlife Refuge Revenue Sharing Act. Such silence is suggestive, because Congress was concerned that the Department have sufficient funds to make the increased payments mandated by the amendments.13 See 1964 S. Rep. 12 (statement of Secretary Udall); 1964 H. R. Rep. 11. Congress might be expected to have mentioned a change wrought through the amendments which would increase refuge revenues by amounts exceeding total existing refuge revenues.14
During deliberations on the amendments, the Fish and Wildlife Service presented to Senate and House Committees tables showing present payments to counties containing refuges, and payments estimated under the proposed amendments. 1964 S. Rep. 13; 1964 H. R. Rep. 3. The relevant table shows no change in the expected payments to the Borough of Kenai Peninsula. This table assumed that oil and gas revenues were governed by the Mineral Leasing Act of 1920 both before and after the amendments.15
*272The inference seems inescapable that Congress in 1964 did not intend by the insertion of “minerals” in § 401 (a) of the Wildlife Refuge Revenue Sharing Act to subject revenues from oil leases on reserved refuge lands to its distribution formula. The more reasonable explanation for the intended effect of including “minerals” is provided by the Department of the Interior. The insertion of “minerals” appears first in 1962 in proposed bills supported by the Department as substitutes for other bills then pending before the House and Senate to increase payments to counties. S. 2138, 87th Cong., 1st Sess. (1961); H. R. 13176, 87th Cong., 2d Sess. (1962). In its report to the Committees, the Department offered no particular explanation for this new term, but the Secretary here concedes that this change was included within the proposal’s descriptive category of “various perfecting . . . provisions.” See Letter from Frank P. Briggs, Assistant Secretary of the Interior, June 20, 1962, in S. Rep. No. 1919, 87th Cong., 2d Sess., 13 (1962); H. R. Rep. No. 2499, 87th Cong., 2d Sess., 4 (1962).
The insertion of “minerals” in § 401 (a) could both leave the mineral revenues from reserved lands subject to the Mineral Leasing Act of 1920 and “perfect” § 401 (a) by incorporating prior changes. The 1947 Mineral Leasing Act for Acquired Lands subjected mineral revenues from lands acquired for wildlife refuges to the distribution formula in the 1935 Refuge Act. We hold that Congress inserted “minerals” in the amended § 401 (a) to recognize the effect of the 1947 Act and to make clear that the amended distribution formula applied to mineral revenues from acquired lands. This conclusion draws support from the evident fact that Congress was concerned almost exclusively with problems related to acquired refuge lands in adopting the 1964 amendments.
Finally, the Department of the Interior interpreted the amendments when passed, and for 10 years thereafter, as not altering the distribution formula. The Department’s con*273temporaneous construction carries persuasive weight. Udall v. Tallman, 380 U. S., at 16. Such attention to contemporaneous construction is particularly appropriate in these cases, because the Department first proposed the amendment. See SEC v. Sloan, 436 U. S. 103, 120 (1978). The Department’s current interpretation, being in conflict with its initial position, is entitled to considerably less deference. See General Electric Co. v. Gilbert, 429 U. S. 125, 143 (1976). In these cases, we find it wholly unpersuasive.
IV
In summary, we hold that revenues generated by oil and gas leases on federal wildlife refuges consisting of reserved public lands must be distributed according to the formula provided in § 35 of the Mineral Leasing Act of 1920. Finding no “clearly expressed congressional intention” to repeal this provision by implication, Morton v. Mancari, 417 U. S., at 551, we conclude that the term “minerals” in § 401 (a) of the Wildlife Refuge Revenue Sharing Act applies only to minerals on acquired refuge lands. Accordingly, the judgment of the Court of Appeals is affirmed.
It is so ordered.
Today, the Kenai Moose Range is the only national wildlife refuge created from public lands where oil is being pumped. See Brief for Federal Petitioners 4, n. 4. Substantial quantities of oil, however, are thought to underlie other reserved refuge lands in Alaska.
Between 1966 and 1976, Kenai Range generated more than $57 million in oil lease revenues. App. 64. In 1964, Kenai Range generated more than $3.8 million in revenues from oil and gas leases. In that same year, refuges on reserved public land in the contiguous 48 States generated $3,143 in oil and gas revenues. App. to Brief for Federal Petitioners la-2a. In interpreting Congress’ directions for distribution of oil revenues from reserved refuge lands, it should be remembered that historically Kenai alone has generated such revenues.
In pertinent part, the current § 35, as set forth in 30 U. S. C. § 191, provides:
“All money received from sales, bonuses, royalties, and rentals of the public lands under the provisions of this chapter . . . shall be paid into the Treasury of the United States; ... of those from Alaska ... 90 per cen-tum thereof shall be paid to the State of Alaska for disposition by the legislature . . . .”
States other than Alaska receive only 50% of public land mineral revenues under the Act. Ibid.
By its terms, the Mineral Leasing Act applies to specified minerals, including oil and gas, on all lands owned by the United States, except those lands excluded by the Act. 30 U. S. C. § 181. See Udall v. Tallman, 380 U. S. 1, 4, and n. 3 (1965).
Prior to 1964, § 401 governed distribution of revenues from “the sale or other disposition of surplus wildlife, or of timber, hay, grass, or other spontaneous products of the soil, shell, sand, or gravel, and from other privileges on refuges.” Act of June 15, 1935, ch. 261, 49 Stat. 378, 383. The current version of § 401 (a) is given in the text, infra, at 265.
Section 401 (c) currently provides:
“(1) The Secretary shall pay out the fund, for each fiscal year ... , to each county in which is situated any fee area whichever of the following amounts is greater:
“(A) An amount equal to the product of 75 cents multiplied by the total acreage of that portion of the fee area which is located within such county.
“(B) An amount equal to three-fourths of 1 per centum of the fair market value, as determined by the Secretary, of that portion of the fee area . . . which is located within such county.
“ (C) An amount equal to 25 per centum of the net receipts collected by the Secretary in connection with operation of and management of such fee area during the fiscal year ....
“(2) At the end of each fiscal year the Secretary shall pay out of the fund for such fiscal year to each county in which any reserve area is situated, an amount equal to 25 per centum of the net receipts collected by the Secretary in connection with the operation and management of such area during such fiscal year . . . 16 U. S. C. § 715s (c) (1976 ed., Supp. III).
Section 401 (b) allows the Secretary to pay any expenses related to revenue production or distribution from this fund. Section 401 (e) pro*263vides that funds remaining after expenses and the States are paid are transferred to the Migratory Bird Conservation Fund, established for the laudable purpose of purchasing migratory bird refuges.
Since this litigation commenced in 1976, 90% of oil and gas revenues from the Kenai Range has been paid into an escrow account that now contains more than $23 million. Brief for Federal Petitioners 4, n. 4. In addition to declaratory relief, Kenai Borough sought an accounting of revenues paid to the State since 1964 under the Mineral Leasing Act of 1920 but allegedly due the Borough, and recovery of such payments. The State sought a resumption of accustomed payments under the Mineral Leasing Act..
In general, “acquired lands are those granted or sold to the United States by a State or citizen and public domain lands were usually never in state or private ownership.” Wallis v. Pan American Petroleum Corp., 384 U. S. 63, 65, n. 2 (1966). The Mineral Leasing Act of 1920 applies only to public lands. Id., at 65.
In 1978, Congress rejected new amendments to §401 (a) that would have defined minerals as “including, but not limited to, crude petroleum and natural gas.” H. R. 8394, 95th Cong., 2d Sess. (1978). The House Report recommending this bill stated that the language was added to “insure” that after the effective date oil and gas revenues from Kenai would be distributed according to the formula in §401 (c). H. R. Rep. No. 95-1197, p. 8 (1978). The Report disclaims any intention to affect *265the outcome of these cases, then pending in the Court of Appeals. Ibid. The Senate then rejected even this amendment, Members stating that it would be inappropriate to malee any judgment about the proper allocation of these resources while these cases were still in the courts. 124 Cong. Rec. 31436-31440 (1970) (remarks of Sen. Culver and Sen. Gravel).
The sole issue that has been before the courts during this five years of litigation is the intent of Congress in adding the single term “minerals” to the statute in 1964. Congress declined to clarify its intent in 1978. Accordingly, we are left to resolve by judicial construction what should be addressed as a question of legislative policy judgment: the appropriate distribution among federal, state, and local governments of natural resource revenues.
“Of course it is true that the words used, even in their literal sense, are the primary, and ordinarily the most reliable, source of interpreting the meaning of any writing: be it a statute, a contract, or anything else. But it is one of the surest indexes of a mature and developed jurisprudence not to make a fortress out of the dictionary; but to remember that statutes always have some purpose or object to accomplish, whose sympathetic and imaginative discovery is the surest guide to their meaning.” Cabell v. Markham, 148 F. 2d 737, 739 (CA2) (L. Hand, J.), aff’d, 326 U. S. 404 (1945).
The Secretary speculates that Congress in 1964 probably assumed that oil and gas revenues from refuges on reserved lands were governed by the 1935 Refuge Act. The basis for this argument is language in the 1935 Refuge Act, continued today, that the Act governed the disposition of "shell, sand, or gravel, and from other privileges on refuges.” See n. 4, supra. It sometimes was contended that “other privileges” included oil and gas leases. See Memorandum of July 6, 1951, Chief Counsel of the Fish and Wildlife Service, App. 87.
As noted, the Comptroller General-rejected this contention in 1942 and 1951. For the reasons elaborated in the text, we believe that it was understood by Congress that the 1935 Refuge Act did not govern the leasing of minerals.' Indeed, even the 1946 opinion of the Solicitor of the Department of the Interior that the provision authorized oil leases on acquired refuge lands, App. 68, is contradicted by Congress’ passage of the Mineral Leasing Act for Acquired Lands, Act of Aug. 7, 1947, ch. 513, 61 Stat. 913, 30 U. S. C. § 351 et seq., which subsequently conferred this very authority on the Department. See also 40 Op. Atty. Gen. 9 (1941).
The dissent also speculates — inconsistently, we think — that Congress embraced this often discredited interpretation of the 1935 Refuge Act, post, at 279-280, n. 3. The dissent criticizes the Court for concluding that Congress’ insertion of "minerals” in § 401 (a) did not change pre-existing law. Post, at 278-279. The dissent then explains that Congress added “minerals” in 1964 not to change the law, but to reaffirm that the 1935 Refuge Act already governed disposition of oil revenues from reserved refuge lands. Post, at 279-280, n. 3. In other words, the dissent contradicts itself and joins us in positing that the addition of “minerals” was never intended to work a substantive change, but disagrees merely about what the law provided prior to the 1964 amendments.
The Secretary argues that Tallman's construction of the Mineral Leasing Act should not now be binding, because the Court did not need to construe the Act. This is incorrect. The Court was required to determine that the Secretary had statutory authority to issue oil leases on refuges withdrawn from public lands, before it could reach the question whether the Executive Orders withdrawing the refuge lands limited that authority. The Court examined the language of § 1 of the Act and found that it gave the Secretary the requisite authority. See 380 U. S., at 4, n. 3.
The 1964 payment formula was liberalized further in 1978. Pub. L. 95-469, § 1(a)(3), 92 Stat. 1319. See n. 5, supra (quoting present law).
The silence of Congress may provide a treacherous guide to its intent. Scripps-Howard Radio, Inc. v. FCC, 316 U. S. 4, 11 (1942). Here, however, it is almost inconceivable that Congress knowingly would have changed substantially a longstanding formula for distribution of substantial funds without a word of comment. In 1978, Congress inserted “sal-monoid carcass[e]s” into the list of resources governed by § 401 (a) of the Wildlife Refuge Revenue Sharing Act. Pub. L. 95-469, § 1(a)(1), 92 Stat. 1319. Even for this comparatively trivial addition, Congress explicitly stated, “[s]almonoid carcasses have been included to allow for the sale of salmon used in hatchery operations.” H. R. Rep. No. 95-1197, p. 8 (1978).
In 1963, net receipts from the national wildlife system totaled $2,350,000. 1964 H. R. Rep. 11. In 1964, revenues from oil and gas leases in the Kenai Moose Range exceeded $3,800,000. App. to Brief for Federal Petitioners 2a.
The table indicated that 1963 payments to the Kenai Peninsula Borough under the Wildlife Refuge Revenue Sharing Act, amended or unamended, totaled $1,768. 1964 H. R. Rep. 3. This figure cannot include 25% of the revenues from oil and gas leases. See n. 14, supra.