We posit that Supreme Court oral arguments provide justices with useful information that influences their final votes on the merits. To examine the role of these proceedings, we ask the following questions: (1) what factors influence the quality of arguments presented to the Court; and, more importantly, (2) does the quality of a lawyer's oral argument affect the justices' final votes on the merits? We answer these questions by utilizing a unique data source - evaluations Justice Blackmun made of the quality of oral arguments presented to the justices. Our analysis shows that Justice Blackmun's grading of attorneys is somewhat influenced by conventional indicators of the credibility of attorneys and are not simply the product of Justice Blackmun's ideological leanings. We thus suggest they can plausibly be seen as measuring the quality of oral argument. We further show that the probability of a justice voting for a litigant increases dramatically if that litigant's lawyer presents better oral arguments than the competing counsel. These results therefore indicate that this element of the Court's decisional process affects final votes on the merits, and it has implications for how other elite decision makers evaluate and use information.