Wild oat, a troublesome weed in cereals, infests about 11 million hectares of cropland in the United States. Diversifying cereal production with alternative crops, such as yellow mustard and canola, can provide flexibility in cropping systems, decrease production risks, and allow for effective weed suppression. The objective of the study was to quantify the competitive ability of yellow mustard and canola relative to wild oat in addition series field experiments, which were conducted in 1999 and 2000 near Genesee, ID. Biomass and seed production of wild oat were reduced 67 and 80%, respectively, in mixtures with yellow mustard, which was three to four times greater than the reduction in corresponding mixtures with canola. In addition, yellow mustard reduced the biomass and seed production of wild oat equally regardless of wild oat density. In contrast, the competitive effect of canola on wild oat biomass decreased 5 to 10 times when wild oat density increased from 100 to 200 plants m−2. Yellow mustard at all densities and at both biomass harvests suppressed wild oat biomass and seed production similarly. But suppression of wild oat by canola increased as canola density increased, and canola plants were more competitive at the flowering stage than at the rosette stage. Wild oat had little or no effect on yellow mustard seed yield but reduced canola seed yield 37%, when averaged over canola densities. Additionally, the oil content of canola seed was reduced 0.4% for every 1% of wild oat seed in the harvested seed. Models developed in this study accurately predicted plant populations of yellow mustard and canola that provided optimal weed suppression and crop yield for different wild oat populations.