Using the ECOPATH II software, a 15-compartment model was constructed to estimate biomass transfers in the Gulf of Mexico continental shelf ecosystem under steady-state conditions and using present, known catch rates. The purpose of the exercise was to evaluate the ecological realism of estimated of prey and predator biomasses that were made in the previous paper. The approach was to set manually biomass and consumption per unit biomass for most compartments based on the best available information and let the software calculate production per unit biomass and respiration per unit biomass. Since the software maintains conservation of matter, the plausibility of the modelling results gave an indication of the realism of the original biomass estimates. Results suggested that the original biomass estimates, except those for macrocrustaceans (shrimp and crabs), were reasonable.