A fluid composition is described for extreme pressure applications. The fluid composition includes a base oil, and an additive composition comprising sulfurized fatty oil in an amount sufficient to provide at least 1,000 ppm sulfur to the fluid composition, and dialkyl thiadiazole in an amount sufficient to provide at least 500 ppm sulfur to the fluid composition. Fluids containing these respective amounts of sulfurized fatty oil and dialkyl thiadiazole exhibit failure loads which equal or exceed 794 kg (1750 pounds) at 100°C and 150°C, respectively, as measured according to a Falex EP test of ASTM D-3233.