We conducted an experiment on a group of captive rhesus macaques (Macaca mulatta) in which we manipulated both food size and interfood distance independently to examine which factor was more important in causing aggressive competition. For each of 254 trials, the monkeys were offered simultaneously two apple pieces ranging in size from 1 to 40 g at interfood distances ranging from 1 to 5 m. In contrast to other studies, food size and interfood distance were not conflated in this study. Multiple regression analyses revealed that food size was a better predictor of aggression whereas interfood distance was a better predictor of the ability to monopolize foods. Growing evidence suggests that factors such as food size, quality and depletion time are more important than interfood distance in influencing aggression within groups.