Why do people frequently cooperate in defiance of their immediate incentives? One explanation is that individuals are conditionally cooperative. As an explanation of behavior in one-shot settings, such preferences require individuals to be able to discern their opponents' preferences. Using data from a television game show, we provide evidence about how individuals implement conditionally cooperative preferences. We show that contestants forgo large sums of money to be cooperative; they cooperate at heightened levels when their opponents are predictably cooperative; and they fare worse when their observable characteristics predict less cooperation because opponents avoid cooperating with them.