The participation of individual African lions, Panthera leo, during 64 communal hunts of four prey species was measured to quantify the extent to which lions cooperate and the factors affecting the degree of cooperation. The extent of individual participation in communal hunts varied significantly. Finite mixture models were used to determine the probability that each lion's behaviour belonged to each of three strategies: 'refraining' (non-participation in hunts), 'conforming' (active participation in groups in which all individuals behaved similarly) and 'pursuing' (active participation in groups where individual behaviour varies). Our analysis reveals two important trends. First, males refrain more and pursue less than females. Second, refraining during a group hunt is more common during hunts of prey that appear to be easier to capture: lions are more likely to refrain during hunts of wart hog, Phacochoerus aethiopicus, and less likely to refrain during hunts of zebra, Equus burchelli, and buffalo, Syncerus caffer. Of the alternatives considered, the data indicate that refraining is 'cheating' and that lions exhibiting this strategy are thus exploiting the hunting behaviour of their companions. These results are discussed in the framework of a recent game-theoretical model of cooperative hunting.