A previous study indicated photosynthesis of Bouteloua gracilis and Buchloe dactylaides has a similar response to temperature, achieving their maximum at high temperatures. Together, photosynthesis response and phenology determine no temporal segregation in growth for these 2 grasses. To study competitive abilities, we performed 2 experiments that combined both species to compare intra- and interspecific competition. One experiment was planted in a small homogeneous area and ran for 3 years; the other occupied an area 9-times larger and lasted 2 years. In each, we planted target plants of both species in a honeycomb design to get a combination of species, to control plant size and neighborhood asymmetries at the start of the experiment, and to represent field conditions. Steel cylinders placed around half the target plants reduced belowground competition. Plant biomass and seed production of plants growing inside the cylinders (reduced dcompetition) were higher than target plants growing in competition. In neither experiment was relative growth rate affected by competition in the last year. There was no difference between the two species in intra- and interspecific relative competition intensity (calculated with biomass); seed production was more variable than biomass. In some years, intra- and interspecific competition equally reduced seed production; in others, the interspecific competition effect was more intense. Competition theory predicts intraspecific competition must be greater than interspecific for 2 species with similar requirements to achieve coexistence. Results suggest intense competition between these 2 species with similar environmental requirements and, in general, these species are not affected differentially by intra- and interspecific competition.