In this paper, the performance of CO2 capture from methane was studied at various operating conditions including high pressure to investigate the effects of a heavy hydrocarbon (pentane) on the CO2 capture and separation performance of membranes. Based on this study's findings, the permeance and selectivity for CO2 and CH4 under wet conditions (with heavy hydrocarbon) decrease compared to dry conditions (without heavy hydrocarbon). Therefore, the presence of pentane as a heavy hydrocarbon in a natural gas stream decreases the performance of CO2 capture when using membrane processes. © 2014 Elsevier Ltd.