On December 10, 2013, a packed audience listened to 90 minutes of oral argument before the U.S. Supreme Court regarding the U.S. Environmental Protection Agency’s (EPA) currently vacated Cross-State Air Pollution Rule (CSAPR). HGS has previously reported (here, here, and here) on the U.S. Court of Appeals for the District of Columbia Circuit vacatur of CSAPR and the U.S. Supreme Court’s decision to grant review of that ruling. Three HGS attorneys— Robert Manning, Joseph Brown, and Mohammad Jazil — have been actively involved throughout CSAPR’s rule development and subsequent litigation and attended the argument along with representatives of other parties in the case. Eight Justices heard argument (Justice Alito recused himself), with no apparent majority leaning in favor of either side. With only eight Justices participating, there is the possibility of a four-four split decision, in which case the D.C. Circuit’s ruling would be affirmed. Of the three questions presented on review, the Justices had pointed questions for both sides on the two merits issues raised, but did not ask a single question regarding whether the D.C. Circuit lacked jurisdiction to issue its ruling in the first instance, as asserted by EPA. Thus, while an outcome on either merits issue seems difficult to predict, it appears likely that the D.C. Circuit’s decision is at least safe from reversal on jurisdictional grounds. A decision from the Court is likely by June 2014.