Abstract: A lubricant, fuel or other composition comprising an organo-substituted benzophenone in which the latter compound acts as a lubricant base stock, a blend stock, an additive solubility enhancer and/or a deposit reducing agent, and is defined as having at least one ring carbon atom of its benzophenone moiety bonded to an organo radical which is a hydrocarbyl radical containing 1 to about 60 carbon atoms, or such a hydrocarbyl radical modified to contain additional oxygen, nitrogen and/or sulfur. Compositions containing such an organo-substituted benzophenone as the base fluid possess excellent resistance to deposition under severe conditions as well as outstanding thermal and oxidative stabilities.