This study took a pragmatic approach to examining the effects of task difficulty on L2 oral output. Twenty native English speakers and 59 Japanese students of English at two different proficiency levels produced speech acts of requests and refusals in a role play task. The task had two situation types based on three social variables: interlocutors' power difference (P), social distance (D), and the degree of imposition (R). In one situation type, the power relationship was equal, the distance was small, and the degree of imposition was small (PDR-low). In the other situation type, the listener had greater power, the distance was large, and the degree of imposition was also large (PDR-high). The participants' production was analyzed for overall appropriateness (rated on a 6-point scale), planning time, and speech rate. Results showed that L2 learners produced PDR-low speech acts significantly more easily and quickly, but little difference was observed in native speakers' production. There was a significant proficiency effect on appropriateness ratings and speech rate, but not on planning time. "Post hoc" analyses showed that each group demonstrated different patterns in the choice of linguistic expressions over the two situation types, indicating the noteworthy impact of situational variation on oral speech act production.