This study reports 144 new analyses of short-chain aliphatic acid anions (acetate, propionate, butyrate, and valerate) in formation waters from eight localities: Eastern Venezuelan Basin, Denver Basin, Eastern Green River Basin (Red Desert and Washakie Basins, Wamsutter Arch), San Juan Basin, Piceance Basin, Raton Basin, Gulf Coast Basin, and the Western Overthrust. Reservoir temperature does not predict total or relative abundance of aliphatic acid anions, but does predict maximum total concentrations of these species. Maximum concentrations increase to ~90°C. Above ~90°C, maximum concentrations decrease. Above ~250°C, maximum concentrations should not exceed ~1 mg/1. The general order of dominance is acetate > propionate > butyrate > valerate, but for coal-associated waters is propionate > acetate > butyrate > valerate. Lack of longer-chain aliphatic acid anion dominance over acetate at low reservoir temperatures may suggest hydrologie communication with deeper reservoirs.