This paper describes the principal features of solvent resistant nanofiltration, and in particular its potential in fuel processing. Experimental data for both fuel simulants and a representative petrol fuel are presented to illustrate the salient features. The solute rejection mechanism for low polarity mixtures was size exclusion with a membrane cut-off in the region of 1-2 nm. The extent of solute rejection was dependent on the degree of membrane crosslinking, the membrane swelling induced by the feed and the applied (filtration) pressure. Nanofiltration experiments with the petrol fuel showed a good correlation with the data obtained for the fuel simulants, both in terms of permeate flux and solute rejection. Provided that higher polarity oxygenates were not present in the fuel, it was possible to remove undesirable poly-nuclear aromatic and organometallic solutes to an extent that was sufficient to reduce valve deposits (by 64%) and emissions gases (by up to 17%) in engine tests. These improvements significantly better the changes in engine performance that are brought about by the more traditional addition of fuel additives such as detergents. The technology provides a method for removing undesirable solutes from mixtures without the need for excessive energy input. (C) 2008 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.