This paper presents the development of the mathematical equations used for modeling immersion frying of an infinite slab. Immersion frying was viewed as a moving boundary problem similar to that found in freezing and freeze-drying. The infinite slab was divined into two regions, the crust and core, and macroscopic balances were used to develop the governing partial differential equations for heat and mass transfer in each region. Flux relations were proposed for the heat and mass transfer and incorporated into the partial differential equations. The final set of equations consisted of four non-linear partial differential equations and appropriate boundary conditions and initial conditions.