This study employed an experimental design intended to be an analog to the workplace to examine a person by situation interactive effect on OCBs, which were evaluated as prosocial behaviors. This study also sought to provide initial empirical support for the two-stage social cognitive model of OCBs proposed by Hauenstein and Kalanick (2008). Participants were 194 undergraduates. The study was a 2 (Helpfulness) by 2 (Fairness) design. After completing distracter tasks 1 and 2, participants received either a helpfulness prime or a control prime (task 3). Participants then either experienced either a fair manipulation or an unfair manipulation. Results indicated a distinction between the decision to help and helping effort, which has not been thoroughly examined in literature on OCBs. Results revealed main effects for the helpfulness prime and fairness manipulation on the decision to engage in helping. The nature of these effects was that participants helped more when they were primed with helpfulness and when they experienced fairness. However, once helping commenced, there was an interactive effect between helpfulness and fairness such that the helpfulness prime had a stronger effect on participants treated unfairly. Implications for future research on OCBs are discussed.