The volume emissivity has been calculated for thirty-six type III solar radio bursts obtained from approximately 6.5 year of Imp 8 and ISEE 1 satellite data. Although the emissivities for these events vary over a large range, all the emissivities decrease rapidly with increasing heliocentric radial distance. The best fit power law for the emissivity, using the average power law index for all events analyzed, is J=J0R-6.0, with J0=1.5†10-24W m-3 sr-1. This best fit emissivity is used to estimate the expected radial variation of the plasma oscillations responsible for the type III radio emission.