This investigation relates to the study of reactions between liquid and solid phases. This report describes the study of the influence of pressure on the rate of ablation of solid urea by liquid nitric acid in the range of 1-30 bars. The experimental results obtained are first given, followed by an attempt at interpretation by introducing a relation between pressure and the temperature at the reaction interface and by postulating the existence of an adsorbed layer on the surface of the solid. Three distinct ablation patterns have been uncovered, one at low flow rates where the ablation rate is independent of pressure and is a function of flow only; one at high flow rates where the ablation rate is independent of flow, is a function of pressure only and becomes constant at high pressures; and an intermediate pattern where the ablation rate is a function both of flow and pressure. The results obtained are exactly analogous to those noted in gas-solid ablation, which makes it possible to extend the theoretical interpretation to these phenomena.