Previous research has discovered a curious phenomenon: groups cooperate less than individuals in a deterministic prisoner’s dilemma game, but cooperate more than individuals when uncertainty is introduced into the game. We conducted two studies to examine three possible processes that might drive groups to be more cooperative than individuals in reducing risks: group risk concern, group cooperation expectation, and pressure to conform to social norms. We found that ex post guilt aversion and ex-post blame avoidance cause group members to be more risk concerned than individuals under uncertainty. These concerns drive groups to choose the cooperation (and risk-reduction) strategy more frequently than individuals. Groups also have higher cooperation expectations for their corresponding groups than individuals have for their corresponding individuals. We found no evidence of pressure to conform to social norms driving groups to be more cooperative than individuals.