A reformer system (11) having a hydrodesulfurizer (12) provides desulfurized natural gas feedstock to a catalytic steam reformer (16), the outflow of which is treated by a water gas shift reactor (20) and optionally a preferential CO oxidizer (58) to provide reformate gas (28, 28a) having high hydrogen and moderate carbon dioxide content. To avoid damage to the hydrodesulfurizer from overheating, any deleterious hydrogen reactants, such as the oxygen in peak shave gas or olefins, in the non-desulfurized natural gas feedstock (35) are reacted (38) with hydrogen (28, 28a; 71) to convert them to alkanes (e.g., ethylene and propylene to ethane and propane) and to convert oxygen to water in a catalytic reactor (38) having no sulfide sorbent, and cooled (46), below a temperature which would damage the reactor, by evaporative cooling with pressurized hot water (42). Hydrogen for the desulfurizer and the hydrogen reactions may be provided as recycle reformate (28, 28a) or from a mini-CPO (67), or from other sources.