A power transmission fluid composition for extreme pressure applications. The power transmission fluid includes a base oil, and an additive composition containing an extreme pressure performance improving amount of an ester of phosphonic acid of the formula: where R1 is a hydrocarbyl group containing from about 8 to about 24 carbon atoms, R2 and R3 are independently selected from hydrogen and a hydrocarbyl group containing from about 1 to about 8 carbon atoms, provided that no more than one of R2 and R3 is hydrogen, a succinimide dispersant, and, optionally, a metal-based detergent. The optional detergent is substantially devoid of calcium cations.