The results of photometric studies of solutions of various crude oil blends in aromatic and aliphatic solvents are reported. Compatible and incompatible combinations of components are indicated and a quantitative correlation between the optical density of the solutions and the composition of the crude oil blends is established. It is demonstrated that regardless of the nature of the solvent, the light absorption coefficient K of compatible blends is inversely proportional to the percentage ratio between resins and sum of paraffins and asphaltenes (R/P + As) and directly proportional to the density of the blends.