Method implemented by a computer to determine the quantity and/or the quality of the hydrocarbons present in a sedimentary basin, the said hydrocarbons having been generated by the maturation of the organic matter of a source rock of the said basin, by means of a numerical basin simulator containing a kinetic model, the said kinetic model being applied with kinetic parameters in order to reproduce the transformation of the organic matter into at least one chemical compound under the effect of an increase in temperature, on the basis of kinetic parameters relating to the said source rock and relating to a first compositional representation, characterized in that kinetic parameters relating to the said source rock and relating to a second compositional representation are determined by applying at least the following steps by means of the said kinetic model, the said first and second compositional representations being defined by a different number of classes of chemical compounds: A) from kinetic parameters relating to at least one reference source rock and relating to the said second compositional representation, and from kinetic parameters relating to a reference rock and relating to the said second compositional representation, a compositional reference for the said second compositional representation is determined in the form of an evolution in a proportion of each of the chemical compounds of the said second compositional representation as a function of a level of transformation of the said reference rock; B) from the said kinetic parameters relating to the said source rock and relating to the said first compositional representation, and from the said compositional reference determined for the said second compositional representation, kinetic parameters relating to the said source rock and relating to the said second compositional representation are determined; and in that the said quantity and/or the said quality of the said hydrocarbons is determined from the said simulator containing at least the said kinetic model, the said kinetic model being applied with the said kinetic parameters relating to the said source rock for the said second compositional representation. characterized in that kinetic parameters relating to the said source rock and relating to a second compositional representation are determined by applying at least the following steps by means of the said kinetic model, the said first and second compositional representations being defined by a different number of classes of chemical compounds: A) from kinetic parameters relating to at least one reference source rock and relating to the said second compositional representation, and from kinetic parameters relating to a reference rock and relating to the said second compositional representation, a compositional reference for the said second compositional representation is determined in the form of an evolution in a proportion of each of the chemical compounds of the said second compositional representation as a function of a level of transformation of the said reference rock; B) from the said kinetic parameters relating to the said source rock and relating to the said first compositional representation, and from the said compositional reference determined for the said second compositional representation, kinetic parameters relating to the said source rock and relating to the said second compositional representation are determined; A) from kinetic parameters relating to at least one reference source rock and relating to the said second compositional representation, and from kinetic parameters relating to a reference rock and relating to the said second compositional representation, a compositional reference for the said second compositional representation is determined in the form of an evolution in a proportion of each of the chemical compounds of the said second compositional representation as a function of a level of transformation of the said reference rock; B) from the said kinetic parameters relating to the said source rock and relating to the said first compositional representation, and from the said compositional reference determined for the said second compositional representation, kinetic parameters relating to the said source rock and relating to the said second compositional representation are determined; and in that the said quantity and/or the said quality of the said hydrocarbons is determined from the said simulator containing at least the said kinetic model, the said kinetic model being applied with the said kinetic parameters relating to the said source rock for the said second compositional representation.