Many scholars have long contributed to making the instruction of oral production more effectively. This study compared three task types (information-gap, reasoning-gap, and opinion-gap tasks) and two cognitive styles (field-independence and field-dependence) regarding their effects on English as a foreign language (EFL( learners’ oral production linguistic complexity. The current study was quantitative in research methodology and followed the comparison group design. Initially, 230 Iranian learners were selected using convenience sampling. After the participants sat the proficiency test, the number of participants was reduced to 180 BA students at the university of Mohaghegh Ardabili and Islamic Azad University, Ardabil Branch. They were randomly divided into six experimental groups. Two groups were randomly assigned to field-independent (FI) and field-dependent (FD) information-gap tasks, the next two groups to FI and FD reasoning-gap tasks, and the other two groups to FI and FD opinion-gap task types. Each group consisted of 30 advanced EFL learners and was taught oral production using one of the above-mentioned task types. Michigan test of English Language Proficiency test (Phakiti, 2003) and group embedded figures test (Witkin et al., 1971) were used to determine proficiency level and measure cognitive styles. A two-way ANCOVA (analysis of covariance) procedure was run to examine the data. The results revealed significant differences among task types and cognitive styles, with FD learners and opinion-gap task being the most effective on EFL Learners' oral production linguistic complexity. The interaction between cognitive styles and task types is more likely to account for language learners’ oral performance.