The F-value distribution in a batch retort processing of in-pack conduction heating foods resulting from the variability of four processing factors (initial temperature, heating time, headspace and external heat transfer coefficient) was determined by mathematical modelling. Three hundred combinations were generated from normally distributed values for each factor, following the Monte Carlo approach. The retort temperature was assumed the same for all containers and the F-value at the geometrical centre of containers of different dimensions was calculated by solving the governing heat transfer equations using finite elements. It was found that in the range tested the variability of the heating time and of the external heat transfer coefficient had the biggest impact on the F-value distribution and that the head space variability had a negligible impact. It was also found that although each influencing factor had a normal distribution, the F-value distribution was not normal, showing a significant tailing, being well described by a gamma function. (C) 2000