Studies quantifying the grouping and forage-selection patterns of scimitar-horned oryx (Oryx dammah) in Texas or in their native range, where they are probably extinct, are scarce. This oryx is less dimorphic in size than most ruminants; dimorphism in size is associated with intersexual differences in grouping patterns and diet. We hypothesized that males and females associate in mixed-sex groups and do not exhibit intersexual differences in selection of forage. Our study was conducted at Mason Mountain Wildlife Management Area, Mason County, Texas, during June 2006–April 2007. Grouping patterns were measured from systematic surveys conducted from vehicles at dawn and in the afternoon in 6 different months. We collected fecal samples from individuals of known sex and assessed diet using fragments of plants in fecal samples. We measured seasonal availability of food in areas where fecal samples were collected. We encountered mixed-sex groups more often than same-sex groups and we detected no difference between sexes in diet. However, there were differences among seasons in selection of forage. The majority of diet was grasses, such as Sporobolus and Eragrostis, and forbs. Our study supported expectations based on similar-sized males and females.