Apparent heat transfer coefficients (h) were determined for the come-up, heating, and cooling cycles of thermal processing for retortable pouches heated by circulating hot water under overriding air pressure. Values for h were converged on by a computer-based optimization method that incorporated process data, a finite difference model, and optimization criteria. For retortable pouches thermally processed in circulating water under overriding air pressure, h values for the come-up, heating, and cooling cycles were found not significantly different (95% confidence). This indicates that in mathematical models a constant h value may be assumed for the three thermal processing stages. Also, there was no significant difference between h values for aluminum foil/plastic laminate pouches and all-plastic pouches during the combined come-up and heating stages. Thus, the same h value for a given process is applicable to either pouch type.