Study of molecular weight distributions provides a more informative and discriminating approach to uncovering the nature of the gel effect than analysis of rate or molecular weight average data. Analysis of pseudoinstantaneous molecular weight distributions, calculated from cumulative molecular weight distributions, is used in this work to provide new insights into the nature of the gel effect in free-radical polymerization. Pseudoinstantaneous molecular weight distributions from several methyl methacrylate polymerizations have been studied, revealing three distinct instantaneous molecular weight distributions are produced at different times during the polymerization; a single distribution characterizes the low-conversion regime, while two distributions are shown to exist during the high-conversion regime. The evolution of these constituent distributions over the course of the polymerization is described, and the implications of this behavior as it pertains to the gel effect are discussed.