Nucleation in the presence of an inert carrier gas is investigated by molecular dynamics simulation of an immiscible binary mixture. The distribution of clusters in the quenched and quasiequilibrium state is used to localize the critical nucleation size, which is 100 particles for a nucleation time of approximately 50 ns. The density profiles in clusters before and at onset of nucleation are determined from an ensemble of 25 independent nucleations. The density profiles show that the inert carrier gas particles, which have a particle fraction of 0.75 in the quenched state, are squeezed out of the clusters before onset of nucleation. This is in agreement with the classical nucleation theory. (C) 2003 American Institute of Physics.