We describe a new, simple apparatus that permits accurate measurement of reactive organic carbon vapor pressure from heavy crude oils when used with a gas chromatograph. The apparatus is analogous to the Reid vapor pressure apparatus that is used for vapor pressure measurement of light hydrocarbons. This system overcomes many of the shortcomings experienced when the Reid method is applied to heavy crudes. We explain the operation of the system and present results from measurement of heavy crudes from Southern California. Measurements on oil samples collected from storage tanks agreed well with analysis of headspace gases in the tanks.