A new expanded ＇regional＇ method (expanded regional formation rate analysis, ERRA), which allows quantitative correlation between product formation rates at various reactant conversion levels with the nature and strength of active sites of solid acid catalysts is presented. This method permits to determine whether the reaction products are stable or unstable, and primary or secondary over each active center. The intrinsic activity of the active sites grouped in six regions (three by their strength : weak, medium and strong, and two by their nature : Bronsted and Lewis) was evaluated from the overall formation rates on a set of catalysts, similarly to the MRR method. The ERRA method was applied to the conversion of methylcyclohexane over MFI and MEL zeolites catalysts type ZSM-5, ZSM-11, ZBS-11 (boronsilicate zeolite) and SABO-11. A good correlation was found between the experimental data and the prediction obtained with this method.