The problem of determining the pressure and composition profiles of natural gas under centrifugation is formulated and solved as the minimization of a modified Helmholtz function that includes the contribution of the centrifugal field. Fluid properties are calculated using the Peng-Robinson equation of state but the procedure can be readily extended to use other thermodynamic models. The simulations indicate that there may be a liquid phase in the centrifugation cell. However, even in cases with a single gas phase, there are large differences in composition, pressure, and density between the regions close to and away from the rotation axis, confirming the idea that centrifugation might be a useful method for removing contaminants from natural gas. (c) 2005 Elsevier Ltd. All rights reserved.