We examined variation in mating system structure, male and female behavior, and the opportunity for sexual selection over multiple years in two populations of the Gulf Coast toad, Bufo valliceps, in south-central Texas. There was substantial variation in mating system structure among years and among sites. Duration of calling activity ranged between seven and 29 nights, chorus sizes ranged between two and 65 males, and male densities ranged between 0.01 and 0.52 males/m of shoreline. Overall, operational sex ratio was negatively related to both chorus size and male density. Males did not exhibit satellite behavior, and active searching behavior was rare. Females usually appeared to freely select mates, and single males were never observed attempting to displace an amplectant male. Male mating success was strongly skewed in all years at both sites; within a year >60% of males did not mate, but some males mated with as many as four females. The opportunity for selection arising from variance in male mating success varied both among years and among sites within a year. Our observations suggest that the potential for sexual selection by female choice is high, despite the somewhat explosive breeding season of this species.