Plaintiff appeals from a judgment dismissing his petition for a writ of habeas corpus. ORS 34.310 to ORS 34.730. He seeks immediate release from custody under ORS 34.700(1). We dismiss plaintiffs petition as moot.
This case has previously been before us. Jones v. Armenakis, 144 Or App 23, 925 P2d 130 (1996), mod 146 Or App 198, 932 P2d 99 (1997). The petition for a writ of habeas corpus was filed in November 1994. The order on appeal before us postpones a parole release date in 1994. Plaintiff appealed after the trial court dismissed plaintiffs petition on its own motion. We held that the summary dismissal was error and remanded. To give context to the reader, we quote from our first opinions:
“Plaintiffs petition alleged: In 1985, he was convicted of armed robbery and robbery; in 1986 and 1993, the Board of Parole (Board) established his parole release date as October 18,1994; on September 25,1994, he received a ‘disciplinary misconduct’ report for assault, disobedience of an order and disrespect; ‘on or before’ October 11, 1994, an employee of the Department of Corrections recommended that his parole release date be reset; that recommendation was ‘contrary’ to Department of Correction’s rules on prison term modification, OAR 291-97-130(1) to (6), because he had not been found guilty of a violation; on October 11, 1994, the Board rescinded his parole release date without notice or hearing ‘pending [receipt of a] disciplinary report from Department of Corrections’; on October 17, 1994, he was found guilty of violating various rules of prohibited prisoner conduct; on November 4, 1994, he received an order from the Board ‘noting’ that the Board had received the disciplinary report requesting extension of the parole release date and setting a postponement hearing for November 30,1994.
“Plaintiff alleged that the above ‘procedures,’ which used the October 11 employee recommendation to rescind or postpone his release date, were in contravention of ORS 144.125(2) and violated his state and federal rights against ex post facto laws, equal privileges and immunities, equal protection of the laws and due process.” 144 Or App at 25.
*229After our opinion issued, the then-defendant Armenakis petitioned for reconsideration, which we allowed. We reiterated that we could not affirm a summary dismissal of a petition for habeas corpus “[w]hen, as here, the court fails to enter the required reasons as to why the allegations lack merit * * 146 Or App at 200. On remand, the trial court issued an order to show cause why the writ should not be allowed. Defendant moved to dismiss the petition as moot based on a subsequent order1 by the parole board postponing plaintiffs parole release date to October 1998. The trial court agreed with defendant’s motion and dismissed the petition in April 1997 on the ground that the order of which plaintiff complains was no longer in effect. Plaintiff challenges that ruling by this appeal.
We agree with the trial court that plaintiffs petition is moot. A habeas corpus writ commands a custodian to bring a petitioner before the court to inquire into the legality of the imprisonment at the time that the petition is filed. Penrod/Brown v. Cupp, 283 Or 21, 581 P2d 934 (1978); see also Payton v. Thompson, 156 Or App 217, 968 P2d 388 (1998) (holding that the remedy of habeas corpus is not available when there is no entitlement to release on the date that the petition is filed). Also, our decision in Meriweather v. Board of Parole, 140 Or App 415, 915 P2d 467 (1996), is instructive on the issue of mootness. There, the plaintiff sought judicial review of an order of the parole board establishing a. parole consideration date. During the pendency of review, the date passed. One of the plaintiffs allegations was that the board had erred by refusing to accept a psychological evaluation that contended that the plaintiff’s dangerous mental condition was in remission. We held that the plaintiffs claim was now moot, because the earlier order had been superseded by a subsequent order based on a new report that the petitioner’s dangerous condition was not absent or in remission. We relied on the general principle that a case becomes moot when, because of a change in circumstances, a decision would resolve merely an abstract question without practical effect. That reasoning applies to plaintiffs application for a writ of *230habeas corpus in this case. The relief that plaintiff seeks is release on parole. His entitlement to that relief is predicated on the 1994 board order that has been superseded. Any decision about its legality would resolve merely an abstract question without practical effect.
The dissent would hold otherwise. First, it posits that once the Department of Corrections (DOC) acquires custody of an inmate, the sentencing judgment has no effect other than to set the outer limit of custody. Then it asserts that the defendant’s present custody of plaintiff is dependent on the 1994 order, which it contends was “invalid.” It reasons that because the board applied rules for release in 1994 that constituted an ex post facto application, the 1996 order based on plaintiffs custodial status under the 1994 order is also invalid, thereby mandating plaintiffs release on parole under ORS 144.245(1). However, ORS 144.245(1) provides:
“When the State Board of Parole and Post-Prison Supervision has set a date on which a prisoner is to be released upon parole, the prisoner shall he released on that date unless the prisoner on that date remains subject to an unexpired minimum term during which the prisoner is not eligible for parole, in which case the prisoner shall not be released until the expiration of the minimum term.” (Emphasis added.)
In other words, the statute does nothing more than authorize the release of the inmate on parole on the date set by the board when that date arrives.
Moreover, the dissent’s premise that defendant’s present custody of plaintiff is predicated on the validity of the 1994 release order results from a misunderstanding of how the statutes governing incarceration by DOC and release on parole by the parole board work together in executing a sentence from a trial court. DOC’s custody of plaintiff was and continues to be pursuant to the judgments that imposed his sentences. ORS chapter 137 sets forth DOC’s authority in that regard. ORS 137.310 authorizes DOC to execute the sentence contained within a judgment entered by the trial court. ORS 137.1242 provides for the commitment of a felon to the *231legal and physical custody of DOC. ORS 137.320 requires the sheriff to deliver the defendant to the DOC’s institution to which the defendant is assigned, together with a copy of sentencing judgment. Upon receipt of the judgment, the Department computes the duration of the defendant’s sentence and executes the judgment by retaining custody of the defendant until he or she has completed the sentence. ORS 137.370.
ORS chapter 144 expresses the parole board’s authority in connection with the DOC’s authority under ORS chapter 137. ORS 144.050* *3 authorizes the release on parole of any inmate who was committed to the Department for an offense committed prior to November 1, 1989. ORS 144.120 requires the board to hold an initial parole hearing within six months of the commitment of an inmate to the Corrections Department and to set an initial release date. ORS 144.245 authorizes release by DOC on the initial date unless the board acts to extend the release date before the release date occurs. The release of an inmate on parole serves to interrupt DOC’s custody, but it does not negate the sentence. The sentence authorizes DOC’s custody until the defendant completes the sentence either by serving it in the custody of DOC or by serving it on parole. Thus, in concept, release on parole acts as an alternative means of serving a sentence. Rather than serving it entirely in DOC’s custody, the inmate is permitted to serve part of the sentence on parole. In the event that an inmate is unsuccessful in serving the remainder of his sentence on parole, “[t]he board may, in its discretion, suspend or revoke parole if it determines that parole is not in the best interest of the parolee, or in the best interest of society.” ORS 144.270(2)(g). The effect of a revocation of parole is that the prisoner returns to the custody of DOC to continue to serve the sentence as imposed by the trial court.
*232It follows that when ORS chapters 137 and 144 are read together, the sentence in a judgment continues to have efficacy, even though a prisoner is released on parole and that, contrary to the dissent’s assertion, DOC’s authority to incarcerate a prisoner is not vitiated by an unlawful parole release order. Rather, the parole board’s exercise of its authority to release an inmate on parole determines where and how a convicted defendant will serve the sentence that has been imposed and is being executed at a particular time. At most, the unlawfulness of a parole release order requires the board to reconsider the date it has set for release. It does not ipso facto reinstate the earlier release order or affect the authority of DOC, a different agency, to hold the inmate in custody pursuant to a lawful sentence that has yet to be completed.
Here, the parole board undertook in 1994 to review plaintiffs initial release date before the date of his scheduled release. It decided to extend the release date, pursuant to its authority under ORS 144.125, before the date for scheduled release arrived. Although the parole board’s action may have involved an ex post facto application of the statutory release criteria not in effect at the time that plaintiff committed his crime, the mandatory release provisions of ORS 144.245(1) were not triggered by the Board’s decision. That statute mandates release on parole when the superintendent has in hand an order from the parole board that establishes a particular date for release and the date for release arrives. Until both of those events occur, the trial court’s judgment requires the superintendent to keep a prisoner in custody under the provisions of ORS chapter 137. What the superintendent had in hand, at the time in 1994 when plaintiff was initially scheduled for release, was an unchallenged order that extended the date of his release on parole to 1996. Even if that order was invalid, the board was entitled to reconsider the postponement of parole under the proper criteria as an exercise of its statutory authority. Pursuant to plaintiffs sentence, the only authority that DOC had at the time was to continue to hold plaintiff in custody until the board told it to release him.
The dissent relies on several federal court cases in support of its argument that the 1994 order continues to have collateral consequences. The holdings in those cases differ *233significantly from the issue here because they involve the enhancement of sentences as a result of prior convictions that are under collateral attack. In this case, there has been no increase in plaintiffs sentence because of a prior conviction. Plaintiffs sentence is what it is, regardless of the board’s 1994 order postponing plaintiffs release on parole. Because the remedy of habeas corpus focuses on whether a plaintiff is entitled to immediate release at the time that the petition is filed, the trial court did not err when it dismissed plaintiffs petition. Until the parole board establishes a date for release that occurs when an order for release is in effect, defendant is without authority to release plaintiff under the sentencing judgment that authorizes his custody.4 In plaintiffs case, those two events have never coincided. Consequently, the provisions of ORS 144.245(1) have never been triggered. In sum, plaintiffs request that we now determine the constitutionality of the 1994 parole release order would require us to resolve an abstract question without practical fact in light of the superseding orders of the board that have extended his parole release date to October 1998.
Petition for writ of habeas corpus dismissed as moot.
Plaintiff initiated a habeas corpus proceeding regarding that order on July 8, 1996. Relief was denied by the trial court and an appeal is currently pending.
At the time plaintiff was convicted, OES 137.124(1) provided:
“If the court imposes a sentence of imprisonment upon conviction of a felony, it shall not designate the correctional facility in which the defendant is to *231be confined but shall commit the defendant to the legal and physical custody of the Corrections Division.”
ORS 144.050 provided:
“Subject to applicable laws, the State Board of Parole may authorize any inmate, who is committed to the legal and physical custody of the Corrections Division to go upon parole subject to being arrested and detained under written order of the board or as provided in ORS 144.350. The state board may establish rules and regulations applicable to parole.”
Had the 1994 order extending plaintiffs release date to 1996 been successfully challenged while it was in effect, it would not have vitiated the sentence. Rather, a successful challenge would have resulted in remand to the parole board for it to apply the correct criteria and to determine a new release date. See, e.g., Meadows v. Schiedler, 143 Or App 213, 221, 924 P2d 314 (1996) (holding that the parole board was required to consider whether plaintiffs parole should be postponed under the criteria in effect at the time the plaintiff committed his crime).