Monte Carlo simulations are reported on the sorption and motion of small gas molecules (CH4 and CO2) in poly(octadecyl acrylate), a typical comb-like polymer with biphasic structure. Calculations were performed using a computational procedure recently developed by us, which is suitable to simulate the motion and sorption of small molecules in dense comb-like polymers. To our knowledge, the problem of gas transport in comb-like polymers using explicit penetrant molecules is for the first time studied by computational techniques. The study involves more than 12 million Monte Carlo steps of systems constituted by more than 1470 explicit atoms/pseudoatoms. Solubility coefficients are discussed by comparison with recently reported experimental data. (C) 2003 Elsevier Science Ltd. All rights reserved.