We calculate effective recombination coefficients for the formation of the 5g-4f lines of O III in the intermediate coupling scheme. Photoionization data for the 5g levels calculated using the R-matrix method are used to derive their recombination coefficients. Cascading from higher states is included, allowing for the effects of finite electron density in a hydrogenic approximation. We explicitly include the distribution of population between the two ground levels of O^3+^ in the calculation of the line intensities. The results are presented as a simple programmable formula allowing the calculation of recombination line intensities for electron temperatures, T_e_ in the range 5000-20000K and electron densities, N_e_ in the range 10^2^-10^6^cm^-3^.