Choice research has shown that human participants often prefer situations that allow selection among alternatives (free-choice) to situations that do not (forced-choice). Researchers have observed preference for free-choice even when the magnitude and probability of reward is equal across free- and forced-choice situations. Researchers have questioned why participants prefer having the opportunity to choose when it does not result in more desirable outcomes. One possible explanation is that the free-choice situation acts as an illusory discriminative stimulus that signals a greater chance of obtaining reward. This may be due to a reinforcement history in which a positive correlation exists between the chance of obtaining a reward and the number of options available. No research has been done with human participants that examines the possible effects of an illusory contingency on preference for free-choice. In the present experiment, we attempted to reduce or eliminate the effects an illusory contingency by providing participants with certain rewards for their choices; thereby eliminating any ambiguity related to reward delivery. Preferences for free- vs. forced-choice were compared under certain and uncertain reward probabilities. Forty-four college students participated and their choice preferences were examined under a concurrent-chains schedule of reinforcement in which they gained points for selecting images of cards on a computer screen. Half of the participants were assigned to an ABAB (A = certain, B = uncertain) condition order and the other half to BABA. Participants preferred free-choice under the uncertain condition, but not under the certain condition. Thus, our results demonstrate that preference for free-choice is influenced by reinforcement probability and  support the hypothesis that free-choice preference may be due to an illusory contingency, which may be eliminated when reward is certain.