In this article, an extracorporeal membrane oxygenator (ECMO) is simulated in 2D geometry using computational fluid dynamics (CFD). Momentum and mass transport equations were solved for the laminar flow regime (30 < Re < 130 for the blood channel) using the finite element method. In this study, the software COMSOL was used as the solver. To this end, the main problem of ECMO devices is the pressure drop and the risk of thrombus formation due to blood stagnation, so to solve this problem, the oxygen transfer rate to the blood should be increased. Therefore, in the present study, to optimize the oxygen transfer rate of the blood, three basic parameters were examined: blood flow velocity, oxygen velocity, and membrane thickness. Blood flow was considered at five different velocities (0.2, 0.4, 0.5, 0.6, and 0.8 mm/s). Results showed that increased blood flow velocity adversely affected oxygen permeability, increasing oxygen permeability from about 60% at 0.2 mm/s to about 24% at 0.9 mm/s. In addition, five different membrane thicknesses (0.04, 0.06, 0.08, 0.2, and 0.3 mm) were investigated, and, as expected, better oxygen exchange occurred as the membrane thickness decreased. We also found that the diffusion rate is about 40% for the 0.4 mm/s thin films and about 25% for the same inlet velocity and larger film thickness. Furthermore, the oxygen diffusivity increases from 28% to 38% as the oxygen gas velocity increases. However, oxygen velocities above 0.8 mm/s should not be used, as the range of oxygen diffusivity variation decreases with higher oxygen gas velocities.