We report the results of simulating two multicusp volume negative ion sources in which plasma parameters, hydrogen vibrational spectra, and in one case the negative ion density, have been measured. We find generally good quantitative and qualitative agreement between experiment and theory for the basic discharge parameters. Good agreement is also found for atomic density, although the wall recombination coefficient &ggr;(H) is 0.05 in one source and 0.5 in the other. The calculated densities of vibrationally excited states withv‘≥5 are higher than the measured densities, but the calculated negative ion densities are lower than available measurements. Possible causes for these discrepancies are suggested. Fundamental modifications to the model may be necessary, and we have discussed two possibilities: a suprathermal rotational spectrum, and a spatial gradient in vibrational excitation (due to elastic collisions which can localize the effect of vibrational wall cooling near the wall).