The kinetic equations for the formation of the lumps of the gasoline produced (C-5(+) fraction), paraffins (C-5-C-8), xylenes (o-xylene, m-xylene and p-xylene) and aromatics (benzene, toluene, C-9-C-11) in the transformation of syngas on Cr2O3-ZnO/ZSM5 bifunctional catalyst have been established as a function of the concentration of both reactants (CO and H-2) and CO2 byproduct. The effect of the operating conditions on the RON and on the molecular weight of the gasoline has been studied by experimentation in an integral fixed bed reactor in the range between 10 and 50 atm and between 300 and 425 degrees C. The octane index increases with Cr/Zn atomic ratio of the Cr2O3-ZnO metallic function, with Si/Al ratio of the HZSM5 zeolite, with space time and with the CO/H-2 molar ratio in the feed, in that order, whereas it passes through a maximum with pressure (at 20 atm) and with temperature (at 375 degrees C). On the other hand, the molecular weight of the gasoline increases with the Cr/Zn atomic ratio, pressure, CO/H2 molar ratio and space time, and decreases with the Si/Al ratio and temperature.