Abstract: The invention is a method of predicting the amount and the composition of fluids produced by mineral reactions operating within a sedimentary basin and trapped with hydrocarbons in reservoirs. Geological data characteristic of the basin are acquired and a representation of the basin by a grid is constructed. The evolution of a depth of burial (z), a temperature (T), a pore pressure (P), a volume (V) and a porosity ? at successive ages (ti) representative of the geological history of the basin is then calculated for at least one set of cells of the grid, using a basin model and the geological data. A mineralogical or chemical rock composition is determined in each cell of the set of cells from the geological data of the basin. The amount and the composition of fluids of mineral origin is determined within the set of cells using a geochemical model and an equation of state, from the parameters, the composition and a thermodynamic database.