The hydrodesulfurization characteristics of a residual fuel prepared from Wilmington, California, crude oil were determined at temperatures from 600 deg. to 900 deg. F, pressures of 200 to 800 psig, and space velocities from 0.2 to 2.0Vo/vc/hr, using cobalt molybdate type catalysts. A prediction equation, developed from the experimental data, satisfactorily predicts the fraction of total sulfur that can be removed under any combination of operating conditions within the ranges investigated. Yields and properties of the low-sulfur product are correlated with the fraction of total sulfur removed. Kinetic calculations show that the apparent reaction order and activation energy change with space velocity and temperature.