with whom Mr. Justice Brennan and Mr. Justice Rehnquist join, concurring in part and dissenting in part.
The Washington Tanker Law at issue here has three operative provisions: (1) a requirement that every oil tanker of 50.000 deadweight tons (DWT) or larger employ a pilot licensed by the State of Washington while navigating Puget Sound and adjacent waters, Wash. Rev. Code § 88,16.180 (Supp. 1975); (2) a requirement that every oil tanker of from 40.000 to 125,000 DWT either possess certain safety features or *181utilize tug escorts while operating in Puget Sound, § 88.16.190 (2); and (3) a size limitation, barring tankers in excess of 125,000 DWT from the Sound, § 88.16.190 (1).
I agree with the Court that the pilotage requirement is pre-empted only with respect to enrolled vessels. I also agree that the tug-escort requirement is fully valid, at least until such time as the Secretary of Transportation or his delegate promulgates a federal tug-escort rule or decides, after full consideration, that no such rule is necessary. I therefore join Parts I, II, III, Y, and VII of the Court’s opinion.
In the current posture of this case, however, I see no need to speculate, as the Court does, on the validity of the safety features alternative to the tug requirement. Since the effective date of the Tanker Law, all tankers — including those owned or chartered by appellees — have employed tug escorts rather than attempting to satisfy the alternative safety requirements. The relative expense of compliance, moreover, makes it extremely unlikely, at least for the foreseeable future, that any tankers will be constructed or redesigned to meet the law’s requirements.1 Indeed, the Court itself concludes that § 88.16.190 (2) “may be viewed as simply a tug-escort requirement since it does not have the effect of forcing compliance with the design specifications set forth in the provision.” Ante, at 179; see ante, at 173 n. 25, and 180. Accordingly, I cannot join Part IV of the Court’s opinion.
I also cannot agree with the Court’s conclusion in Part VI of its opinion that the size limitation contained in the Tanker Law *182is invalid under the Supremacy Clause. To reach this conclusion, the Court relies primarily on an analysis of Title I of the PWSA and the Secretary of Transportation’s actions thereunder. I agree with the Court that the Secretary has authority to establish vessel size limitations based on the characteristics of particular waters,2 and that a State is not free to impose more stringent requirements once the Secretary has exercised that authority or has decided, after balancing all of the relevant factors, that a size limitation would not be appropriate. On the other hand, Title I does not by its own force pre-empt all state regulation of vessel size, since it “merely authorizes and does not require the Secretary to issue regulations to implement the provisions of the Title.” Ante, at 171. Thus, as the Court notes, “[t]he pertinent inquiry at this point . . . [is] whether the Secretary, through his delegate, has addressed and acted upon the question of size limitations.” Ante, at 174.
The Court concludes that the Secretary’s delegate, the Coast Guard, has in fact considered the issue of size limitations for Puget Sound and reached a judgment contrary to the one embodied in the Tanker Law. Under well-established principles, however, state law should be displaced “ 'only to the extent necessary to protect the achievement of the aims of’ ” *183federal law; whenever possible, we should “reconcile 'the operation of both statutory schemes with one another rather than holding [the state scheme] completely ousted.’ ” Merrill Lynch, Pierce, Fenner & Smith v. Ware, 414 U. S. 117, 127 (1973), quoting Silver v. New York Stock Exchange, 373 U. S. 341, 361, 357 (1963); accord, De Canas v. Bica, 424 U. S. 351, 357-358, n. 5 (1976). Viewed in light of these principles, the record simply does not support the Court’s finding of conflict between state and federal law.
The Coast Guard’s unwritten “local navigation rule,” which prohibits passage of more than one 70,000 DWT vessel through Rosario Strait at any given time, is the sole evidence cited by the Court to show that size limitations for Puget Sound have been considered by federal authorities. Ante, at 174-175. On this record, however, the rule cannot be said to reflect a determination that the size limitations set forth in the Tanker Law are inappropriate or unnecessary. First, there is no indication that in establishing the vessel traffic rule for Rosario Strait the Coast Guard considered the need for promulgating size limitations for the entire Sound.3 Second, even assuming that the Rosario Strait rule resulted from consideration of the size issue with respect to the entire area, appellees have not demon*184strated that the rule evinces a judgment contrary to the provisions of the Tanker Law. Under the express terms of the PWSA, the existence of local vessel-traffic-control schemes must, be weighed in the balance in determining whether, and to what extent, federal size limitations should be imposed.4 There is no evidence in the record that the Rosario Strait “size limitation” was in existence or even under consideration prior to passage of the Tanker Law.5 Thus appellees have left unrebutted the inference that the Coast Guard’s own limited rule was built upon, and is therefore entirely consistent with, the framework already created by the Tanker Law’s restrictions.
Perhaps in recognition of the tenuousness of its finding of conflict with federal regulation under Title I, the Court suggests that the size limitation imposed by the Tanker Law might also be pre-empted under Title II of the PWSA. Ante, at 175. In particular, the Court theorizes that the state rule might be pre-empted if it “represents a state judgment that, as a matter of safety and environmental protection generally, tankers should not exceed 125,000 DWT.” Ibid. (Emphasis added.) It is clear, however, that the Tanker Law was not merely a reaction to the problems arising out of tanker operations in general, but instead was a measure tailored to respond to unique local conditions — in particular, the unusual *185susceptibility of Puget Sound to damage from large oil spills and the peculiar navigational problems associated with tanker operations in the Sound.6 Thus, there is no basis for preemption under Title II.7
*186For similar reasons, I would hold that Washington’s size regulation does not violate the Commerce Clause. Since water depth and other navigational conditions vary from port to port, local regulation of tanker access — like pilotage and tug requirements, and other harbor and river regulation — is certainly appropriate, and perhaps even necessary, in the absence of determinative federal action. See, e. g., Cooley v. Board of Wardens, 12 How. 299, 319 (1852); Packet Co. v. Catlettsburg, 105 U. S. 559, 562-563 (1882). Appellees have not demonstrated that the Tanker Law’s size limit is an irrational or ineffective means of promoting safety and environmental pro*187tection,8 nor have they shown that the provision imposes any substantial burden on interstate or foreign commerce.9 Consequently, it is clear that appellees have not carried their burden of showing that the provision’s impact on interstate or foreign commerce “is clearly excessive in relation to the putative local benefits.” Pike v. Bruce Church, Inc., 397 U.S. 137, 142 (1970).
I do not find any of appellees’ other arguments persuasive. I would therefore sustain the size limitation imposed by the Tanker Law.
According to the record, no tanker currently afloat has all the design features prescribed by the Tanker Law. Neither Atlantic Richfield nor Seatrain has plans to modify any tankers currently in operation to satisfy the design standards, “because such retrofit is not economically feasible under current and anticipated market conditions.” App. 67. Moreover, the vessels being constructed by Seatrain will not meet the majority of the design requirements, and, as the Court convincingly demonstrates, ante, at 173 n. 25, the Tanker Law is not likely to induce tanker owners to incorporate the specified design features into new tankers.
The relevant provision of Title I states:
“In order to prevent damage to, or the destruction or loss of any vessel, bridge, or other structure on or in the navigable waters of the United States, or any land structure or shore area immediately adjacent to those waters; and to protect the navigable waters and the resources therein from environmental harm resulting from vessel or structure damage, destruction, or loss, the Secretary of the department in which the Coast Guard is operating may—
“(3) control vessel traffic in areas which he determines to be especially hazardous, or under conditions of reduced visibility, adverse weather, vessel congestion, or other hazardous circumstances by—
“(iii) establishing vessel size and speed limitations and vessel operating conditions . . . .” 33 U. S. C. § 1221 (3) (iii) (1970 ed., Supp. V).
The Rosario Strait “size limitation” is not contained in any written rule or regulation, and the record does not indicate how it came into existence. The only reference in the record is the following statement in the stipulation of facts:
“The Coast Guard prohibits the passage of more than one 70,000 DWT vessel thrpugh Rosario Strait in either direction at any given time. During periods of bad weather, the size limitation is reduced to approximately 40,000 DWT.” App. 65.
The Puget Sound Vessel Traffic System, 33 CFR Part 161, Subpart B (1976), as amended, 42 Fed. Reg. 29480 (1977), does not contain any size limitation, and the necessity for such a limitation apparently was never considered during the rulemaking process. See 38 Fed. Reg. 21228 (1973) (notice of proposed rulemaking); 39 Fed. Reg. 25430 (1974) (summary of comments received during rulemaking).
Title I provides in relevant part:
“In determining the need for, and the substance of, any rale or regulation or the exercise of other authority hereunder the Secretary shall, among other things, consider—
“(6) existing vessel traffic control systems, services, and schemes; and “(7) local practices and customs . . . .” 33 U. S. C. § 1222 (e) (1970 ed., Supp. V).
The stipulation of facts does not specify when the size rule for Rosario Strait was established. The rale apparently was in force at the time the stipulation was entered, see n. 3, supra, but the Tanker Law had gone into effect prior to that time.
The Tanker Law contains the following statement of intent and purpose:
“Because of the danger of spills, the legislature finds that the transportation of crude oil and refined petroleum products by tankers on Puget Sound and adjacent waters creates a great potential hazard to important natural resources of the state and to jobs and incomes dependent on these resources.
“The legislature also recognizes Puget Sound and adjacent waters are a relatively confined salt water environment with irregular shorelines and therefore there is a greater than usual likelihood of long-term damage from any large oil spill.
“The legislature further recognizes that certain areas of Puget Sound and adjacent waters have limited space for maneuvering a large oil tanker and that these waters contain many natural navigational obstacles as well as a high density of commercial and pleasure boat traffic.” Wash. Rev. Code § 88.16.170 (Supp. 1975).
The natural navigational hazards in the Sound are compounded by fog, tidal currents, and wind conditions, in addition to the high density of vehicle traffic. App. 69.
Among the “areas . . . [with] limited space for maneuvering a large oil tanker,” referred to by the Washington Legislature, is undoubtedly Rosario Strait. The Strait is less than one-half mile wide at its narrowest point, Exh. G, and portions of the shipping route through the Strait have a depth of only 60 feet. App. 65. (A 190,000 DWT tanker has a draft of approximately 61 feet, and a 120,000 DWT tanker has a draft of approximately 52 feet. Id., at 80.)
In addition to finding the Tanker Law’s size limit to be inconsistent with the PWSA and federal actions thereunder, the Court suggests that “[t]here is some force to the argument” that the size limit conflicts with the tanker construction program established by the Maritime Administration pursuant to the Merchant Marine Act, 1936. Ante, at 179 n. 28. The Court does not rely on this argument, however, and it is totally lacldng in factual basis. While it is true that construction of tankers larger than 125,000 DWT has been subsidized under the program, almost two-thirds of the tankers that have been or are being constructed have been smaller than 125,000 DWT, App. 60; of the remainder, the smallest *186are 225,000 DWT vessels with drafts well in excess of 60 feet — too large to pass through Rosario Strait, see n. 6, supra, or dock at any of the refineries on Puget Sound (Atlantic Richfield’s refinery at Cherry Point has a dockside depth of 55 feet; none of the other five refineries on Puget Sound has sufficient dockside depth even to accommodate tankers as large as 125,000 DWT. App. 47-48, 80).
Appellees advance one final argument for invalidating the 125,000 DWT size limit under the Supremacy Clause. Relying on the well-established proposition that federal enrollment and licensing of a vessel give it authority to engage in coastwise trade and to navigate in state waters, Douglas v. Seacoast Products, Inc., 431 U. S. 265, 276, 280-281 (1977); Gibbons v. Ogden, 9 Wheat. 1, 212-214 (1824), appellees assert that Washington may not exclude from any of its waters tankers that have been enrolled and licensed, or registered, pursuant to the federal vessel registration, enrollment, and licensing laws, 46 U. S. C. §§ 221, 251, 263. Even assuming that registration of a vessel carries with it the same privileges as enrollment and licensing, this argument ignores a proposition as well established as the one relied on by appellees: Notwithstanding the privileges conferred by the federal vessel license, “States may impose upon federal licensees reasonable, nondiscriminatory conservation and environmental protection measures otherwise within their police power.” Douglas v. Seacoast Products, Inc., supra, at 277; see, e. g., Huron Portland Cement Co. v. Detroit, 362 U. S. 440 (1960); Manchester v. Massachusetts, 139 U. S. 240 (1891); Smith v. Maryland, 18 How. 71 (1855). The Tanker Law’s size limitation appears to be a reasonable environmental protection measure, see n. 8, infra, and it is imposed evenhandedly against both residents and nonresidents of the State.
The stipulation quoted by the Court, ante, at 176 n. 27, merely establishes that there is good-faith dispute as to whether exclusion of large tankers will in fact reduce the risk of oil spillage in Puget Sound. A showing that there is conflicting evidence is not sufficient to undercut the presumption that a State’s police power has been exercised in a rational manner. See, e. g., Firemen v. Chicago, R. 1. & P. R. Co., 393 U. S. 129, 138-139 (1968).
Exclusion of tankers larger than 125,000 DWT has not resulted in any reduction in the amount of oil processed at the Puget Sound refineries. App. 68. Moreover, according to the record, use of a 120,000 DWT tanker rather than a 150,000 DWT tanker increases the cost of shipping oil from Valdez, Alaska, to Cherry Point by a mere $.02 to $.04 per barrel, id., at 64; and the record does not specify the relevant cost data for the Persian Gulf-Cherry Point route. Finally, appellees offered no concrete evidence of any significant disruption in their tanker operations, or of any decrease in the market value of the tankers that they own, as a result of the Tanker Law’s provisions.