Densities and refractive indices were measured for native crude oils, distillation cuts, and thermo- and hydrocracked oils at 20 degrees C and for some samples up to 60 degrees C, all at atmospheric pressure. These data as well as pure component and crude oil data from the literature were used to develop correlations between the following: the refractive index function (FRI) and density; the thermal and FRI expansion coefficients; and the binary interaction parameters used in mixing rules for the density and FRI of mixtures. The density (or FR[) of the components (or liquids treated as a single component) were both correlated to within 2%. The density (or FRI) of a mixture was fitted also to within 2% using mixing rules with only the known component density (or FM) at 20 degrees C as the input. The mixture density (or FRI) can be predicted to within 4% using only the correlated component density (or FRI) at 20 degrees C. The correlations have yet to be tested at temperatures above 60 degrees C and pressures above atmospheric.