The results of mathematical modeling of fixed-bed catalytic reactors for low temperature low H2O/C steam reforming of propane-methane mixture and two real associated petroleum gases into methane-enriched fuel gas are reported. Three cases of practical interest were considered. In the first case, a lab-scale flow reactor, which is used for kinetic studies, was analyzed under assumption of constant wall/oven temperature. The possibility of noticeable hot and cold zones formation along the bed radius (4 mm) and length (33 mm) was predicted depending on the wall temperature and the ratios of H2O/C3H8 and C3H8/CH4. In the second case, a plant-scale adiabatic reactor was simulated, and the impossibility of conversion of flare gas with high C2+ fraction into fuel mixture with sufficiently high LHV (>31.8 MJ/m3) was predicted even if the post-removal of CO2 was assumed. In the third case, the advantages of a plant-scale tubular reactor against an adiabatic one were revealed for the reforming of “heavy” and “light” associated petroleum gas. The proposed bifunctional role of steam (first as a coolant, second as a reagent) increases the energy efficiency of tubular reformer due to recuperation of heat produced by reaction. The scheme with counter-current flows of reagent and coolant enabled to reduce twice the number of tubes in comparison with concurrent flow, but the catalyst temperature in the hot zone raised by 40°.