We investigated how grass competition is influenced by which species are involved, and the levels of grazing, water (W) availability, and nitrogen (N) availability, as a way to understand how competition influences the dynamics of prairies. We conducted a DeWit greenhouse competition experiment in fall 2003 with these three common C₄ grasses native to Oklahoma prairies: little bluestem (Schizachyrium scoparium), sideoats grama (Bouteloua curtipendula), and indiangrass (Sorghastrum nutans). These grasses were subjected to three clipping treatments to simulate grazing, two W treatments, and two N treatments. We found that: (1) for little bluestem, different aspects of growth were reduced by intraspecific competition, by interspecific competition with sideoats grama, and by the high clipping treatment, but both W addition and N addition increased growth; (2) for sideoats grama, growth was reduced by clipping, but W addition, N addition, and W addition × low clipping increased growth, and (3) for indiangrass, growth increased with W addition and with N addition, but was reduced by intraspecific competition. We conclude that grass seedlings were more affected by the identity of the competitor species and by clipping than by levels of W and N, that intraspecific competition dominated over interspecific competition, and that species × clipping was the most significant interaction effect.