The present invention relates to a process for reducing naphthenic acid content of crude oils and its fractions in the essential absence of oxygen and in the presence of an aqueous base selected from Group IA and IIA hydroxides and ammonium hydroxide and mixtures thereof, a phase transfer agent that is a quaternary onium salt in amounts of from 10−5 to 10−1 at a temperature and pressure effective to produce a treated petroleum feed having a decreased naphthenic acid content and an aqueous phase containing naphthenate salts, phase transfer agent and base.