A procedure has been developed for isolating acids from crude oils by a two-stage scheme. Initially, by gradient elution analysis, the most polar fraction of acid resins is isolated and treated with diazomethane. Then re-elution of this specimen is carried out with the isolation of the fraction of acid esters. The procedure makes it possible to extract acid from small amounts of the specimen. The composition of acids isolated by the method proposed differs little from the composition of the acids obtained by chromatography on silica gel modified with potassium silicate.