This study examines the effects of manipulating task complexity on learners' L2 oral performance. It has a 2x2 mixed design requiring each participant to perform one simple and one complex task (+/- Here-and-Now) under either careful or pressured online planning conditions. 24 first-year undergraduate students majoring in English Language Teaching at an English medium public university in Turkey completed two storytelling tasks based on two picture strips (Heaton, 1966, 1975). The main aim of the study was to measure both separate and combined effects of two-way manipulations of task demands on participants' syntactic complexity levels on L2 performance. Following Norris and Ortega (2009), syntactic complexity was measured with a phrasal complexity measure which is suitable for learners with high proficiency. The study reported no significant differences between groups as well as across two tasks with respect to syntactic complexity. The results are discussed in the light of Robinson's Cognition Hypothesis, Skehan's Limited Attentional Capacity Hypothesis, and participants' proficiency levels.