Adiabatic operation of catalytic fixed-bed reactors for oxidative coupling of methane (OCM) has been simulated using a detailed microkinetic and reactor model. For several catalysts (1%(wt) Sr/La2O3, 10%(wt) La-20%(wt) Sr/CaO, 4%(wt) Sn-2%(wt) Li/MgO, and 12%(wt) Mn-20%(wt) Na2WO4/SiO2), diverse in activity and selectivity toward C2+ products, operating conditions have been determined that maximize C2+ yield at low inlet temperature T-0 (<< 923 K). A prior analysis of light-off curves served as a guideline for optimal operating temperature ranges for each catalyst. Imposing a maximum temperature in the reactor (T-max <= 1273 K) suggested a limit for the catalytic performances, corresponding to 13% CH4 conversion and 61% C2+ selectivity at the reactor outlet for an active (T-0 = 723 K) Sr/La2O3 catalyst, and an improved 19% CH4 conversion and 82% C2+ selectivity for a less active (T-0 = 853 K) NaMnW/SiO2 catalyst. The obtained results indicated catalyst selectivity, rather than activity, as the key parameter for an industrially relevant adiabatic OCM process.