A mixed-propagation picture for the expansion of an ablation plume through a buffer gas at different pressures is proposed after a brief discussion of the available analytical expansion models. Using parameter values deduced by the model the size of carbon clusters formed during plume propagation in helium is evaluated and compared with experimental data. Starting from experiments on silver plume propagation through molecular oxygen the size of silver clusters is predicted. (c) 2007 Elsevier B.V. All rights reserved.