We conduct an experiment on an online game, exploring the effect on gameplay behavior of voluntary commitment devices that allow players to limit their gameplay. Approximately 25% of players use the devices. Median and 75th percentile device users use devices approximately 60 and 100% of the time, respectively. Players who chose to use the device were those who had previously played longer and more frequently than those who chose not to use the device. Offering the commitment devices decreased session length and session frequency by 2.8 and 6.1%, respectively, while increasing weeks of play by 5.5%. Our results are consistent with some players having self-identified self-control problems, leading to longer and more frequent play than they would prefer, and to demand for commitment, and also with commitment devices creating a more rewarding experience, leading to longer-lasting involvement with the game. Our results suggest incentivizing or requiring commitment devices in computer games.