It has been common practice in the petroleum industry to classify petroleum according to base, i.e., paraffin base, intermediate or mixed base, naphthene base and asphalt base, or by property relationships such as correlation index, characterization factor, ect. Several methods for establishing the base or index have been proposed and used, and these relationships have considerable utility in predicting the behavior of stocks in processing and under service conditions. However, it is not possible at the present time to apply similar systems of correlation to shale oils or shale-oil stocks because the required information is not available on the properties of a variety of shale oils and very few data have been developed to indicate the performance of shale-oil stocks either in refining processes or under service conditions. Lacking such a system of correlation, some idea of the problems involved in refining shale oil and the quality of the products that may be obtained therefore can be had from analyses of these oils.