A probability of winning at least one of a plurality of prizes for a contest is dynamically adjusted, given a fixed prize inventory and an a priori unknown number of participants. A variable probability is determined by approximately dividing a current number of participants in the contest by a current number of prizes awarded. The variable probability is dynamically adjusted based on a variable probability multiplier, that is obtained by dividing a current number of winners in a predefined time interval by a remaining number of prizes in the predefined time interval. A prize can be awarded based on the adjusted variable probability.