The study investigates L1 and L2 speakers’ oral fluency across levels of task complexity and input formats to understand the cognitive processes in L2 speech production. Oral fluency is conceptualized as cognitive fluency, measured by frequency of pausing. The study builds on Skehan et al. (2016) hypothesis that pauses ‘within a clause’ suggest difficulties in formulation, and pauses occurring ‘between clauses’ mean problems with conceptualization. Eighty participants carried out two narrative tasks differentiated by complexity and input format. Participants were 40 English L1 speakers and 40 Korean L1 speakers who speak English L2 at an intermediate level. Data were coded for pauses using PRAAT. The findings reveal L2 speakers show increases in frequency of pauses at mid-clause level on more complex tasks. Pauses at end clause were unaffected by complexity for both L1 and L2 speakers. Findings are explained in terms of cognitive fluency, automaticity, and L2 speech production.