A statistical mechanical formula is developed for the bulk viscosity of molecular liquids. It is expressed in terms of the self-diffusion coefficient of the liquid, intermolecular forces, and the site-site pair correlation functions. The density and temperature dependence of the bulk viscosity of carbon dioxide and nitrogen-are calculated therewith: and compared with experimental data wherever possible. In the case, of liquid nitrogen for which experimental data are available the theoretical values of the bulk viscosity are well within the experimental error ranges in almost all: cases. There are no experimental data to compare with the theoretical results for liquid carbon dioxide,but in the light of the comparison for nitrogen and the excellent sheer viscosity results which were obtained in the same line of approach in the previous work the calculated bulk viscosity values of liquid carbon dioxide may be treated as theoretical predictions.