More than 100,000 individuals of C. olitorius were scored for selfing versus outcrossing in various populations, at several locations, over a number of years and seasons. Different marker loci, such as A (d) /a (0), Sh/sh, Cr/cr and Pl/pl, were used to determine the male gametes which had effected fertilization. The results showed that the frequency of outcrossing was extremely variable among loci, crosses and samples within a single locus. The outcrossing parameter, α, was found to differ with years, locations and seasons within years. It was also found that outcrossing, in general, was nonrandom. Nonrandomness was also independent of flowering dates. The amount of outcrossing was directly associated with the frequency of F 2 plants flowering at different dates. A recalculated outcrossing parameter from different authors' reported data, representing different years and locations, has been found to be nonrandom. It was observed that the propensity to outcross was not a simple function of changing gene frequency but was associated with the genotype of individual selected.