Abstract: The acidic components are obtained from Daqing crude oil by saponification, and chromatographed into five fractions on silica gel column. Three polar fractions are methylated in H₂SO₄-CH₃OH and identified by GC-S, respectively. The relative contents and structure of the petroleum carboxylic acids are given. Daqing crude oil contains a variety of C₉～C₂₄ normal and isomeric carboxylic acids. The latter, mainly occurring in the ethyl acetate-acetone fraction, may play vital roles in enhancing the recovery of crude oil.