The number of particles formed in batch emulsion polymerization over wide ranges of emulsifier and initiator concentration has been investigated by computer simulation with a mathematical model developed in a previous paper. The influence of particle coagulation is also considered. The results show that, at low emulsifier concentration, the steady-state particle numberNsis governed by homogeneous nucleation so thatNsincreases slowly with increasing emulsifier concentration [S]. In this range,Nsincreases with increasing monomer polarity. The steep rise inNswith emulsifier concentration after [S] exceeds a critical value suggests a transition from homogeneous nucleation domination to micelle nucleation. The slope of theNsvs [S] relationship increases as the particle coagulation rate constantKfincreases. The powerxin the empirical relationshipNs≊ [S]xdecreases with increasing polarity of monomer in this region. At very high micelle concentration, insufficient radical generation and the increasing tendency for particle coagulation causeN2to be less dependent on emulsifier concentration. These phenomena have been reviewed by Vanderhoff and confirmed by the experimental data presented by Sutterlin. The particle number increases with increasing initiator concentration [I] when [S] is above the CMC. As [I] continues to increase, however,Nsbecomes relatively constant. Experimental data for styrene, butyl acrylate, and methyl acrylate from the literature are compared with the model predictions. Agreement between the theoretical predictions and the experimental data is evident over a wide range of emulsifier and initiator concentrations.