The elastomeric polymer polyisobutylene has a remarkably low permeability to small penetrant molecules, so is often used in applications requiring a barrier to atmospheric gases. The permeation of the atmospheric gases O-2 and N-2 through polyisobutylene membranes has been investigated via a variety of computer simulation methodologies. These include particle insertion and molecular dynamics simulations. Parallel molecular dynamics simulations were carried out both for 3-dimensionally periodic (bulk) and 2-dimensionally periodic (membrane) samples of the polymer melt. Results are compared to both experiment and previous simulation works, with particular emphasis placed upon comparing the gas barrier properties of polyisobutylene with those of polybutadiene. The experimentally noted low permeability of polyisobutylene when compared with polybutadiene is reproduced well by 2-dimensional (membrane) simulations. It is found that the difference in permeability does not stem solely from a reduced solubility or diffusivity, but rather from a reduction in both. (c) 2012 Elsevier B.V. All rights reserved.