This rule finalizes proposed revisions to the regulations governing the major new source review (NSR) programs mandated by parts C and D of title I of the Clean Air Act (CAA). These changes clarify the "reasonable possibility" recordkeeping and reporting standard of the 2002 NSR reform rules. The "reasonable possibility" standard identifies for sources and reviewing authorities the criteria under which an owner or operator of a major stationary source undergoing a physical change or change in the method of operation that does not trigger major NSR permitting requirements must keep records. The standard also specifies the recordkeeping and reporting requirements on such sources. As noted in the proposal, the U.S. Court of Appeals for the DC Circuit in New York v. EPA, 413 F.3d 3 (DC Cir. 2005) (New York) remanded for the EPA either to provide an acceptable explanation for its "reasonable possibility" standard or to devise an appropriately supported alternative. To satisfy the Court's remand, the EPA is clarifying what constitutes "reasonable possibility" and when the "reasonable possibility" recordkeeping requirements apply.