ORDER

Nebraska Public Power District (NPPD) petitions for permission to appeal the order certified by the United States Court of *981Federal Claims in Nebraska Pub. Power Disk v. United States, No. 01-CV-116 as one involving a controlling question of law as to which there is substantial ground for difference of opinion and for which an immediate appeal may materially advance the ultimate termination of the litigation. 28 U.S.C. §§ 1292(d). The United States responds.*

NPPD filed an action in the trial court seeking damages for, inter alia, the Department of Energy’s alleged partial breach of contract. The United States indicated that it wished to present a defense based on a contract provision concerning delays, but that a writ of mandamus issued by the United States Court of Appeals for the District of Columbia Circuit in Northern States Power Co. v. Dept. of Energy, 128 F.3d 754 (D.C.Cir. 1997) precluded it from presenting that defense. After briefing and oral argument, the trial court ruled that the D.C. Circuit’s mandamus order in Northern States is void and thus does not preclude the United States from asserting the contract delay provision as a defense. On NPPD’s motion, the trial court certified its order for interlocutory appeal. NPPD seeks permission to appeal.

In certifying its order for interlocutory appeal, the trial court determined that the order involved a controlling question of law with respect to which there is a substantial ground for difference of opinion and that an immediate appeal may materially advance the ultimate termination of the litigation.

The decision whether to grant a petition for permission to appeal is within this court’s discretion. See In re Convertible Rowing Exerciser Patent Litigation, 903 F.2d 822 (Fed.Cir. 1990). In this case, we conclude that interlocutory appeal is warranted.

Accordingly,

IT IS ORDERED THAT:

The petition for permission to appeal is granted.