There is a substantial body of research into the effects of planning time on second language (L2) oral performance, but different effects were found -- some of them showing increased accuracy, others increased complexity and/or fluency of language. In this study, 30 English as a foreign language learner individually performed a narrative and an argumentative task under planned and unplanned conditions. Then, ten of the participants took part in a retrospective debriefing. Both the oral narratives and retrospective reports were transcribed and analyzed manually. The results revealed that planning led to syntactically more varied but less accurate language whilst fluency remained unaffected. Significant effects of task type could be observed, with argumentation outperforming narration on most measures. In addition, an interaction between planning and task type was statistically proven for almost all measures of fluency and for a single measure of complexity. Furthermore, most participants had positive attitudes towards pre-task planning. The findings also suggest that choosing suitable task-based implementational conditions can assist L2 learners in improving oral performances.