The modeling of soot formation and oxidation by the conditional moment closure (CMC) method is considered. It is particularly focused on the influence of differential diffusion of the soot particles on soot predictions. Most importantly, no changes are made to the soot models that were derived from laminar flame experiments and calculations. Goad to excellent predictions are achieved in lightly sooting turbulent methane-air jet diffusion flames at atmospheric and elevated pressure when differential diffusion is taken into account. Unity Lewis number assumptions yield underpredictions of soot volume fractions by about 40%. Soot oxidation by OR and O-2 can be treated accurately and both oxidation mechanisms are found to be important for soot burnout in downstream regions. (C) 2000 by The Combustion Institute.