This work examines the filtration of soot-in-oil colloid aerosols, utilising both whole filter testing and single fibre force measurements. It was found that the presence of soot increases the equilibrium pressure drop of coalescing filters subject to discontinuous operation; such as those used in engine crankcase ventilation. We have found that this pressure drop increase may be explained by the increase in effective oil viscosity caused by the presence of soot, but that this may not delay the onset of drainage, as the soot was found not to increase droplet displacement forces. Soot accumulation in the filter has been observed, on the same order of magnitude as could be expected due to physical deposition mechanisms. (C) 2012 Elsevier Ltd. All rights reserved.