Junji Yamamoto, a federal prisoner, appeals the denial of his petition for a writ of habeas corpus, claiming that the United States Parole Commission’s use of parole guidelines promulgated after the commission of his crime to determine his parole eligibility violates the constitutional prohibition against ex post facto laws. The district court1 held that the federal parole guidelines are not laws and that the ex post facto clause thus does not apply. As we are convinced the ex post facto clause is not applicable, we affirm.
Yamamoto was sentenced on July 16, 1982, to a seven-year term of imprisonment (eighty-four months) for conspiracy to import and distribute heroin from 1976 through 1979. Yamamoto had his initial parole hearing before a panel of United States Parole Commission hearing examiners on March 24, 1983. Applying the 1983 paroling policy guidelines set forth at 28 C.F.R. § 2.20 (1983), the panel determined that Yamamoto was a very good parole risk and assigned him a salient factor score of ten out of ten. The panel rated Yama-moto’s offense behavior as category eight severity because it involved a conspiracy to import and distribute more than three kilograms of heroin of one hundred percent purity in which Yamamoto had a managerial and proprietary interest. The 1983 parole guidelines provided that an offender with a salient factor score of ten and an offense severity rating of eight should be expected to serve one hundred or more months before release. After determining that a decision outside the guidelines was not warranted in this case, the panel informed Yamamoto that he would continue serving to the expiration of his eighty-four month sentence minus good-time reductions, resulting in a term of imprisonment of fifty-six months.2
After exhausting his administrative appeals, Yamamoto filed a petition for writ of habeas corpus with the United States District Court, contending that the application of the 1983 parole guidelines to an offender convicted of a crime that occurred from 1976 through 1979 violated the ex post facto clause of the United States Constitution, U.S. Const. art. I, § 9, cl. 3. A United States magistrate issued a report recommending dismissal of Yamamoto’s petition on the grounds that the federal parole guidelines are not laws within the meaning of the ex post facto clause. The district court overruled Yamamoto’s exceptions to the magistrate’s report and, adopting its rationale, dismissed Yamamoto’s petition.3 This appeal followed.
*1297The Constitution prohibits Congress from passing any law that “makes an action done before the passing of the law, and which was innocent when done, criminal; * * * [or] changes the punishment, and inflicts a greater punishment, than the law annexed to the crime, when committed.” Colder v. Bull, 3 U.S. (3 Dall.) 386, 390,1 L.Ed. 648 (1798); see U.S. Const. art. I, § 9, cl. 3.4 The ex post facto clause serves both to curtail legislative abuses and to give fair warning of criminal laws and their punishments. Weaver v. Graham, 450 U.S. 24, 29, 101 S.Ct. 960, 964, 67 L.Ed.2d 17 (1981). A law violates the ex post facto clause if it applies retrospectively to events occurring before its enactment and if it is more onerous than the law in effect on the date of the offense. Id. at 30-31, 101 S.Ct. at 965-66.
While the 1983 guidelines are prospective in the sense that they relate to parole discretion to be exercised after their effective date, it is undisputed that application of the 1983 parole guidelines to determine Yama-moto’s parole eligibility fulfills the retro-spectivity requirement of Weaver v. Graham because the 1983 guidelines were not in effect in 1979, the last year of Yama-moto’s conspiracy.5 Yamamoto also argues that the 1983 guidelines are more onerous than the 1979 guidelines in effect when he committed his crime. For an offender with his salient factor score and offense severity rating, Yamamoto contends, the 1979 guidelines recommended a term of imprisonment of forty to fifty-two months before parole, whereas the 1983 guidelines recommend that such an offender serve one hundred or more months before release. Based on the 1983 guidelines, the parole panel determined that Yama-moto should serve his full eighty-four month sentence less good-time reductions, a total of fifty-six months. Thus, Yama-moto contends, the panel’s use of the 1983 guidelines to make his parole determination violated the ex post facto clause because he received a more onerous punishment than he would have received under the guidelines in effect at the time of his crime.
We conclude that there is no ex post facto violation. Our holding that in the circumstances of this case retrospective application of the federal parole guidelines does not offend the ex post facto clause is supported by an impressive line of authority. Eight other circuits and one Supreme Court justice have reached a similar result, although they have not always agreed on the rationale.6 The majority of these courts have held, as the district court did in this case, that the federal parole guidelines are not “laws” within the meaning of the ex post facto clause and that the ex post facto clause thus does not apply.7 Other *1298courts have found that the guidelines merely rationalize the exercise of statutory discretion and that retrospective application of the guidelines thus does not violate the ex post facto clause.8 Some of these cases have held, in the alternative, that the retrospective application of the guidelines does not result in a more onerous punishment and thus does not violate the ex post facto clause.9
Congress has for many years delegated the power to parole federal prisoners to the United States Parole Commission, known until 1976 as the United States Board of Parole.10 The Board considered federal prisoner parole applications without reference to written guidelines until 1972. Then, in response to criticisms that parole decisions were eratic and inconsistent, the Board began to experiment with the use of written guidelines to structure its decision-making process. To accommodate these and other changes in the federal parole system, Congress enacted the Parole Commission and Reorganization Act in 1976, ch. 311, 90 Stat. 219 (codified as amended at 18 U.S.C.A. §§ 4201-4218 (West 1985)). The Act replaced the Board with the Commission, clarified the structure of the parole process, and required the Commission to promulgate and use written guidelines in making parole decisions.
In Hayward v. United States Parole Commission, 659 F.2d 857 (8th Cir.1981), cert. denied, 456 U.S. 935, 102 S.Ct. 1991, 72 L.Ed.2d 454 (1982), we considered whether the use of the newly promulgated parole guidelines to determine the parole eligibility of an offender convicted of a crime that occurred prior to the adoption of the parole guidelines violated the ex post facto clause. Although we expressly declined to decide whether the federal parole guidelines are laws within the meaning of the ex post facto clause, we determined that the parole system in effect at the time the crime was committed (1970-1971) did *1299not give the defendant any expectation of a particular parole system. Id. at 862.11 We therefore held that the retrospective application of the parole guidelines did not violate the ex post facto clause. Id. Implicit in this holding was a finding that, because an offender had no expectation, aside from the constraints imposed by the sentencing judge, as to the length of time he or she would serve before parole prior to the adoption of the written guidelines, the adoption of the written guidelines could not result in a more onerous punishment. While Hayward, supra, and Richardson v. United States Parole Commission, 729 F.2d 1154 (8th Cir.1984), expressly declined to decide whether the federal parole guidelines are laws within the meaning of the ex post facto clause and Rush v. Petrovsky, 756 F.2d 675 (8th Cir.1985), found it unnecessary to consider this issue, we are favorably impressed with the holdings of the several circuits that have so concluded. See supra n. 7. We are also persuaded, however, that it is unnecessary to reach this issue in this case as we are satisfied that Yamamoto had no expectation of a particular parole system at the time the crime was committed, Hayward, 659 F.2d at 862, and that the new guidelines were not more onerous than the old. Accordingly, once again we need not specifically address this issue.
Of importance here is the question whether Congress, in enacting the Parole Commission and Reorganization Act of 1976, so substantially reduced the Commission’s discretion over parole decisions that a prisoner now has an expectation that in making parole decisions the Commission will adhere more firmly to the guidelines. Only then would an upward revision of the guidelines possibly result in a more onerous punishment.12
Although the parole guidelines were intended to reduce the disparity of prison terms for like offenders and offenses, S.Rep. No. 369, 94th Cong., 2d Sess. 18, reprinted in 1976 U.S.Code. Cong. & Ad.News 335, 339-40, Congress clearly intended that parole eligibility determinations would remain a matter of discretion with the Parole Commission. For example, 18 U.S.C. 4206(c) provides that “[t]he Commission may grant or deny release on parole notwithstanding the guidelines referred to in subsection (a) of this section if it determines there is good cause for so doing.” The legislative history of the 1976 Parole Commission and Reorganization Act confirms that Congress intended the Parole Commission to continue to make parole determinations on an individual basis in light of the “nature and circumstances of the offense and the history and characteristics of the prisoner.” H.R.Rep. No. 838, 94th Cong., 2d Sess. 19, 26, reprinted in 1976 U.S.Code Cong. & Ad.News 351, 358; see also id. passim.
Moreover, the regulations promulgated by the Parole Commission clearly indicate that the guidelines are merely guides to agency discretion rather than rigid rules. For example, the statement of general policy preceeding the guidelines provides in pertinent part:
(a) To establish a national paroling policy, promote a more consistent exercise of discretion, and enable fairer and more equitable decision-making without remov*1300ing individual case consideration, the United States Parole Commission has adopted guidelines for parole release consideration.
(b) These guidelines indicate the customary range of time to be served before release for various combinations of offense (severity) and offender (parole prognosis) characteristics. The time ranges specified by the guidelines are established specifically for cases with good institutional adjustment and program progress.
(c) These time ranges are merely guidelines. Where the circumstances warrant, decisions outside of the guidelines (either above or below) may be rendered.
28 C.F.R. § 2.20(a), (b) & (c) (1983). Finally, both the legislative history of the statute authorizing the guidelines and the Parole Commission regulations recognize that the guidelines should be periodically reviewed and revised or modified if decisions frequently go above or below the guidelines’ recommendations. H.R.Rep. No. 838 at 27, reprinted in 1976 U.S.Code Cong. & Ad.News at 360; 28 C.F.R. § 2.20(g) (1983). Offenders are thus given fair warning that the guidelines governing parole determinations are subject to change. See Inglese v. United States Parole Commission, 768 F.2d 932, 936 (7th Cir.1985); see also Weaver v. Graham, 450 U.S. 24, 30, 101 S.Ct. 960, 965, 67 L.Ed.2d 17 (1981) (“Critical to relief under the Ex Post Facto Clause is not an individual’s right to less punishment but the lack of fair notice and governmental restraint when the legislature increases punishment beyond what was prescribed when the crime was consummated”) (emphasis added). In short:
The statute, the parole regulations, and the policy statements contained therein clearly and repeatedly emphasize the discretionary aspect of the decision-making process of parole, particularly in the use of the guidelines. While a heightened standard of review checks this discretion, the Commission’s inherent ability to exercise discretion is not thereby altered.
Inglese, 768 F.2d at 936. In light of Congress’ clearly expressed intent that the guidelines would not significantly restrict the Parole Commission’s discretion in determining the length of time a prisoner should serve before parole, we hold that the Parole Commission’s use of the 1983 federal parole guidelines in making Yama-moto’s parole determination did not result in a more onerous punishment. Accordingly, retroactive application of the guidelines does not violate the ex post facto clause.
In holding that application of the 1983 federal parole guidelines to Yamamoto does not violate the ex post facto clause, we are aware of some limits to our decision. Our decision does not rest on the fact that the guidelines were promulgated by an agency rather than by Congress itself. Clearly, Congress may not, by delegation, escape constitutional limitations on its power. See McCall, 709 F.2d 852, 859 (3d Cir.1983), appeal after remand, 776 F.2d 1156 (3d Cir.1985); Inglese, 768 F.2d at 935. If Congress would be prevented by the ex post facto clause from retroactively revising guidelines of the type involved' here, so too would an agency acting pursuant to congressional mandate. We recognize that some aspects of the parole process, while a matter of discretion, are such that a change in the parole process could violate the ex post facto clause. For example, retrospective application of a statute or rule altering the method for computing “gain time for good conduct” to an inmate who committed a crime before the enactment of the alteration clearly violates the ex post facto clause. Weaver v. Graham, 450 U.S. 24, 35-36, 101 S.Ct. 960, 967-68, 67 L.Ed.2d 17 (1981). Adverse changes in the frequency with which a prisoner may be considered for parole or in the time at which a prisoner first becomes eligible for parole consideration may also violate the ex post facto clause. See United States ex rel. Graham v. United States Parole Commission, 629 F.2d 1040, 1043 (5th Cir.1980) (adverse change in frequency of parole hearing); Rodriquez v. United States Parole Commission, 594 F.2d 170, 175-76 *1301(7th Cir.1979) (adverse change in time at which prisoner becomes eligible for parole consideration).
From what has been said, it follows that the judgment of the district court is affirmed.
. The Honorable William R. Collinson, Senior United States District Judge for the Eastern and Western Districts of Missouri.
. Parole eligibility determinations are made without reference to the credits an offender has earned for good-time served. Briggs v. United States Parole Commission, 736 F.2d 446, 449 (8th Cir.1984).
. Contrary to the magistrate’s recommendation, the district court granted Yamamoto leave to proceed in forma pauperis because it determined that the issue of whether the federal parole eligibility guidelines constitute laws un*1297der the ex post facto clause is one of first impression in the Eighth Circuit.
. The Constitution also prohibits states from passing ex post facto laws. U.S. Const. art. I, § 10, cl. 1.
. In Hayward v. United States Parole Commission, 659 F.2d 857, 862 (8th Cir.1981), cert. denied, 456 U.S. 935, 102 S.Ct. 1991, 72 L.Ed.2d 454 (1982), we held that an ex post facto analysis focuses on the law in effect on the date of the offense, rather than on the law in effect at the time of sentencing.
. See Portley v. Grossman, 444 U.S. 1311, 1312-13, 100 S.Ct. 714, 715, 62 L.Ed.2d 723 (1980) (in chambers opinion of Rehnquist, Circuit Justice denying stay of execution pending review on certiorari of Ninth Circuit’s denial of a writ of habeas corpus); United States ex rel. Forman v. McCall, 776 F.2d 1156, 1163 (3d Cir.1985); Inglese v. U.S. Parole Commission, 768 F.2d 932 at 935-36 (7th Cir.1985); DiNapoli v. Northeast Regional Parole Commission, 764 F.2d 143, 146 (2d Cir.), cert. denied, — U.S. —, 106 S.Ct. 568, 88 L.Ed.2d 553 (1985); Dufresne v. Baer, 744 F.2d 1543, 1549-50 (11th Cir.1984), cert. denied, — U.S. —, 106 S.Ct. 61, 88 L.Ed.2d 49 (1985); Roth v. United States Parole Commission, 724 F.2d 836, 840 (9th Cir.1984); Stroud v. United States Parole Commission, 668 F.2d 843, 847 (5th Cir.1982); Warren v. United States Parole Commission, 659 F.2d 183, 193-97 (D.C.Cir.1981), cert. denied, 455 U.S. 650, 102 S.Ct. 1454, 71 L.Ed.2d 665 (1982); Ruip v. United States, 555 F.2d 1331, 1335-36 (6th Cir.1977).
. See Inglese, 768 F.2d at 935-36; DiNapoli, 764 F.2d at 146; Dufresne, 744 F.2d at 1549-50; Roth, 724 F.2d at 840; Ruip, 555 F.2d at 1335-36; see also United States ex rel. Forman v. McCall, 776 F.2d at 1163 (although initially holding that federal parole guidelines might be deemed "laws" under the ex post facto clause if the Parole Commission applies those guidelines inflexibly, see United States ex rel. Forman v. *1298McCall, 709 F.2d 852, 859-62 (3d Cir.1983), concluding on consideration after remand that as a factual matter, the guidelines are applied with "substantial flexibility” and thus do not constitute "laws”).
This court has declined to determine, or found it unnecessary to consider, whether the federal parole guidelines constitute "laws” within the meaning of the ex post facto clause on three occasions. See Rush v. Petrovsky, 756 F.2d 675 (8th Cir.1985) (per curiam); Richardson v. United States Parole Commission, 729 F.2d 1154, 1156 n.1 (8th Cir.1984) (per curiam); Hayward v. United States Parole Commission, 659 F.2d 857, 862 (8th Cir.1981), cert. denied, 456 U.S. 935, 102 S.Ct. 1991, 72 L.Ed.2d 454 (1982). Instead, in each of those cases, we determined that the federal parole guidelines did not result in a more onerous punishment.
. See Portley, 444 U.S. at 1312, 100 S.Ct. at 715; Warren v. U.S. Parole Commission, 659 F.2d 183 at 195 (D.C.Cir.1981). The Sixth Circuit merely held without further elaboration that “(t]here is no ex post facto violation in the retroactive application of the guidelines.” Stroud, 668 F.2d at 847.
. See Dufresne, 744 F.2d at 1549-50; Warren, 659 F.2d at 193; Raifai v. United States Parole Commission, 586 F.2d 695, 698-99 (9th Cir.1978).
The Supreme Court has twice expressly declined to consider whether retrospective application of the federal parole guidelines violates the ex post facto clause. See United States Parole Commission v. Geraghty, 445 U.S. 388, 390 n.1, 408, 100 S.Ct. 1202, 1205 n. 1, 1214-15, 63 L.Ed.2d 479 (1980); United States v. Addonizio, 442 U.S. 178, 184, 99 S.Ct. 2235, 2239-40, 60 L.Ed.2d 805 (1979). In each of those cases, the Court found it unnecessary to address any part of the ex post facto issue.
. Parole Commission and Reorganization Act, ch. 311, 90 Stat. 219 (1976) (codified as amended at 18 U.S.C.A. §§ 4201-4218 (West 1985)) (repealing and replacing Act of June 25, 1948, P.L. 80-722, ch. 311, §§ 4201-4207, 62 Stat. 683, 854-55, and Act of Aug. 25, 1958, P.L. 85-752, §§ 3-5, 72 Stat. 845-47 (both codified as amended at 18 U.S.C. §§ 4201-4209 (1970)) (repealed 1976)).
The Sentencing Reform Act of 1984 abolishes the parole system and replaces the current sentencing process with a system of sentencing guidelines, effective November 1, 1986. P.L. 98-473, tit. II, ch. II, 98 Stat. 1987; id. at § 218(a)(5), 98 Stat. 2027 (repealing chapter 311, currently codified as amended at 18 U.S. C.A. §§ 4201-4218 (West 1985)). The Parole Commission and current law provisions relating to parole are to remain in effect for five years after the effective date of the Sentencing Reform Act as to any individual convicted of an offense before the effective date of the Act in order to deal with sentences imposed under current sentencing practices. Id. § 235(b)(1), 98 Stat. 2032.
. The statute in effect at the time Hayward committed his offense provided in pertinent part:
If it appears to the Board of Parole from a report by the proper institutional officers or upon application by a prisoner eligible for release on parole, that there is a reasonable probability that such prisoner will live and remain at liberty without violating the laws, and if in the opinion of the Board such release is not incompatible with the welfare of society, the Board may in its discretion authorize the release of such prisoner on parole. 18 U.S.C. § 4203(a) (1970) (emphasis added) (repealed 1976).
. Here the Commission observes that, since Yamamoto's offense involved smuggling more than sixty times the amount of heroin listed in the “Greatest I" category of the 1979 guidelines, the Commission probably would have imposed a parole decision above that guideline. Thus, the Commission argues, there is no showing in fact that a more onerous burden under the 1983 guidelines has resulted.