Thirteen genotypes of Bromus catharticus (prairie grass) were evaluated for forage production over three years using completely randomized trials with six replicates. The genotype x environment interaction was statistically significant and indicates that the behavior of genotypes differs over time. Once this interaction was detected, we used three methodologies to assess the stability of genotypes: Wricke's ecovalence, the Lin and Binns index, and the Eberhart and Russell model. The methods of Lin and Binns and Eberhart and Russell indicate that genotypes 11, 9, 3 and 4 are stable. They also rule out possible selection of genotypes 2, 10, 1 and 12 for lack of stability or poor adaptation. The correlation among these indices was statistically significant (r=0.61). When using Wricke's ecovalence, there is agreement among the indices for the selection of genotypes 9 and 4, which show good stability. There is no agreement with the other two methods for ruling out unstable genotypes. Considering the three methodologies used, the Lin and Binns index is easiest to apply and interpret because higher productivity always correlates with greater stability, and there are no restrictions on the use of regression. However, it is necessary to accumulate more data prior to the widespread use of these methods.