This consolidated appeal involves respondent Department of Transportation’s (‘‘DOT’s’’) interpretation of federal law governing airline service at Love Field airport. Petitioners Dallas Fort Worth International Airport Board (‘‘DFW Board’’), City of Fort Worth (‘‘Fort Worth’’), American Airlines, Inc. (‘‘American’’), City of Dallas (‘‘Dallas’’), Southwest Airlines Company (‘‘Southwest’’), and Love Field Citizens Action Committee (the ‘‘Committee’’) petition for review of DOT’s declaratory, procedural, and reconsideration orders. Legend Airlines, Inc. (‘‘Legend’’), Continental Airlines, Inc. (‘‘Continental’’), and Continental Express, Inc. (‘‘Continental Express’’) have intervened. For the reasons set forth below, we affirm.

   Prior to 1968, Dallas and Fort Worth operated independent and competing airports. One of Dallas’s airports was Love Field. DOT’s predecessor agency, the Civil Aeronautics Board (‘‘CAB’’), found that the competition between Dallas’s and Fort Worth’s airports was harmful. Accordingly, in 1964 CAB ordered the cities to build a jointly operated airport that would serve as the region’s primary airport. The cities responded by creating the DFW Board and by jointly adopting the 1968 Regional Airport Concurrent Bond Ordinance (the ‘‘Ordinance’’). The Ordinance authorized the issuance of bonds to finance the Dallas-Fort Worth Airport (‘‘DFW’’). Of critical importance here is section 9.5 of the Ordinance, which contained the cities’ agreement to ‘‘take such steps as may be necessary, appropriate and legally permissible * * * to provide for the orderly, efficient and effective phase-out at Love Field, Redbird, GSIA and Meacham Field, of any and all Certificated Air Carrier Services, and to transfer such activities to the [DFW] Regional Airport.’’

   The eight CAB-certified air carriers who were using the Dallas and Fort Worth airports * * * [agreed] to move their air services to DFW as specified in the Ordinance. Southwest, which was solely running intrastate flights from Love Field and thus was exempt from CAB certification and pressure, refused to move to DFW and did not sign [the] agreement. Litigation ensued over efforts to force Southwest from Love Field, terminating with our statement that ‘‘Southwest Airlines Co. has a federally declared right to the continued use of and access to Love Field, so long as Love Field remains open.’’ [Citation.]

   Congress deregulated the airline industry in 1978. Shortly thereafter, Southwest applied for permission to provide interstate service between Love Field and New Orleans. CAB granted the application, concluding that it lacked power to deny it. This prompted Congress to intervene by enacting the Wright Amendment. [Citation.] The Wright Amendment generally bans interstate service from Love Field. However, it provides certain exemptions from this ban, two of which are significant here: (1) the commuter airline exemption allows interstate ‘‘air transportation provided by commuter airlines operating aircraft with a passenger capacity of 56 passengers or less’’; and (2) the contiguous state exemption allows flights to and from Louisiana, Arkansas, Oklahoma, and New Mexico, if the flights do not ‘‘provide any through service or ticketing with another air carrier’’ and do not ‘‘offer for sale transportation to or from * * * any point which is outside any such State.’’ [Citation.]

   The Shelby Amendment [enacted in 1997] * * * expanded the contiguous states exemption to allow direct flights between Love Field and airports within Kansas, Alabama, and Mississippi. [Citation.]

   The parties in this case responded in various ways to the Shelby Amendment. Southwest began offering flights between Love Field and Mississippi and Alabama. Legend has announced plans to offer long-haul service to states outside the Love Field service area using large aircraft reconfigured to have less than 57 seats. Continental Express plans to use regional jets with less than 57 seats to fly between Love Field and Cleveland. Continental Express and American offer intrastate flights from Love Field to their hubs, in Houston and Austin respectively.

   In response, Fort Worth sued Dallas, the DFW Board, Legend, Continental, and Continental Express in Texas state court to block the proposed additional service from Love Field. * * *

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   At the urging of several of the parties, and while both the federal and state actions were pending, DOT initiated the interpretative proceeding that is the subject of this petition for review. DOT issued an order informing the parties in this action that it intended to rule on four ‘‘federal law issues’’ and allowing the parties an opportunity to submit comments on these issues. Subsequently, in response to the parties’ initial comments, * * * DOT ultimately issued a ‘‘Declaratory Order’’ resolving the * * * questions it had set forth. Specifically, DOT ruled that:

(i) the City of Fort Worth may not enforce any commitment by the City of Dallas * * * to limit operations at Love Field authorized by federal law, and the proprietary powers of the City of Dallas do not allow it to restrict services at Love Field authorized by federal law; (ii) the ability of the City of Dallas to limit the type of airline service operated at Love Field is preempted by the Wright and Shelby Amendments; (iii) any airline operating aircraft with a passenger capacity of no more than 56 passengers and a gross aircraft weight of no more than 300,000 pounds may operate service with any type of equipment and flights of any length from or to Love Field, notwithstanding any claim that such service violates any agreement between the Cities of Dallas and Fort Worth; (iv) the Dallas-Fort Worth International Airport Board may not enforce any contract provision that allegedly bars an airline from operating interstate airline service at another airport in the Dallas-Fort Worth metropolitan area; and (v) any airline may offer through service between Love Field and any other point to passengers using a flight between Love Field and another point within Texas operated under subsection (a) of the Wright Amendment, as amended by the Shelby Amendment. * * *

   [Citation.] In an accompanying ‘‘Procedural Order,’’ DOT rejected various procedural objections raised by the parties. DOT subsequently reaffirmed its rulings on reconsideration.

* * *

   Several of the parties challenge DOT’s declaratory order on procedural grounds * * * that: DOT violated the Administrative Procedure Act (‘‘APA’’). * * *

   Fort Worth and the DFW Board argue that DOT’s ruling violated the APA in various ways. See § 706 (directing a reviewing court to ‘‘hold unlawful and set aside agency action, findings, and conclusions found to be * * * without observance of procedure required by law’’). Although DOT has already rejected some of these challenges in its earlier rulings, we review de novo DOT’s interpretation and application of the APA. [Citation.]

   Several parties contend that DOT failed to provide them with sufficient notice as required under § 554(b) or, alternatively, § 553, of the APA. We exercise plenary review over whether DOT complied with applicable procedures. [Citation.]

   DOT issued its declaratory order after conducting an informal adjudication, pursuant to its authority under § 554(e) to ‘‘issue a declaratory ruling to terminate a controversy or remove uncertainty.’’ [Citations.] Several parties object to DOT’s failure to adhere to the APA’s notice requirements for formal adjudications. However, in the absence of a statute requiring an agency to conduct its adjudication ‘‘on the record after opportunity for agency hearing,’’[citation], an agency can define its own procedures for conducting an informal adjudication. [Citation.]

   While the APA does not expressly require notice in informal adjudications, courts have inferred a requirement that there be ‘‘some sort of procedures for notice [and] comment* * * as a necessary means of carrying out our responsibility for a thorough and searching review [of agency action].’’ [Citation.] Here, DOT issued an order in which it specified the legal issues on which it would rule, allowed the parties to submit comments on these issues, and extended the comment period at the request of several parties. It then ruled on precisely the issues that it identified. We find that DOT’s actions satisfied the minimum procedural notice requirements. [Citation.]

   Fort Worth contends that DOT failed to comply with § 554(b) by neglecting to notify parties that DOT would also be considering a factual issue: the effect of increased service at Love Field on DFW Airport. This argument fails for two reasons. First, as noted, the formal notice requirement of § 554(b) does not apply to an informal adjudication. Second, the parties were effectively on notice of this issue since it was one that they could reasonably expect to arise given the issues of which DOT gave notice. [Citation.] The fact that Dallas, Continental Express, and Legend all submitted factual evidence to DOT should also have put Fort Worth on notice that it could submit its own factual evidence.

   We also reject the DFW Board’s argument that DOT’s order amounts to a substantive rule subject to the notice and comment provision of § 553. Agencies have discretion to choose between adjudication and rulemaking as a means of setting policy. [Citation.] In determining whether an agency action constituted adjudication or rulemaking, we look to the product of the agency action. We also accord significant deference to an agency’s characterization of its own action. [Citation.] Since the APA defines ‘‘adjudication’’ as the ‘‘agency process for formulating an order,’’ § 551(7), and DOT classifies its ruling as a declaratory order, we find that the agency engaged in adjudication rather than rulemaking. Furthermore, because DOT’s order interpreted the rights of a small number of parties properly before it, DOT did not abuse its discretion by acting through an adjudicatory proceeding. [Citation.]

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   For the foregoing reasons, we DENY the petitions for review and AFFIRM DOT’s orders.