Eastern and Western U.S. and Australian oil shales were retorted in a fixed-bed, bench-scale retorter, using nitrogen and carbon dioxide as sweep gases. The resulting shale oils were chemically characterized by GC/MS techniques. Shale oils extracted by nitrogen and carbon dioxide retorting processes were found to have different chemical compositions, even when applied to the same oil shale samples. The extraction process dependent nature of shale oils is fully assessed in this paper and the information may be used for comparison among various extraction processes as well as for choosing appropriate upgrading processes for the crude shale oils.