Data on sexual consortships in a troop of chacma baboons are analyzed in relation to a priority-of-access model and to critical demographic and social variables. The data show a robust association between adult male rank and mating success, and a close approximation to priority-of-access type mating. Principal findings were: (1) Mating activity peaked during the four most likely days of ovulation, and was greater on conceptive than on nonconceptive cycles. (2) On each day of estrus, males of the alpha rank consorted more frequently than did males of other ranks for both classes of cycles.