Solution properties of several different phosphorus compounds prepared in hydrocarbons of various polarities were studied by dielectric thermal analysis and yielded data as to conductivity and surface reactivity. X-ray photoelectron spectroscopy was performed on steel gear teeth and provided elemental composition as well as thickness of the reacted surface layer. This data was correlated with ASTM test results, A mechanism is proposed that explains the relative phosphorus content and thickness of the protection films on the steel surface. The mechanism is based on correlating the organophosphorus molecular mass and hydrocarbon polarity as it relates to ASTM test results. The same phosphorus compound was blended into several hydrocarbons of differing polarities and was observed to give varying ASTM test results. Several different phosphorus compounds of various molecular masses were blended into the same base fluid and were observed to also give varying ASTM test results,