Recent interest in fuel cells has led to the conceptual design of an ocean floor, fuel cell-based, power generating station fueled by methane from natural gas seeps or from the controlled decomposition of methane hydrates. Because the dissolved oxygen concentration in deep ocean water is too low to provide adequate supplies to a fuel processor and fuel cell, oxygen must be stored onboard the generating station. A lab scale catalytic autothermal reformer capable of operating at pressures of 6–50bar was constructed and tested. The objective of the experimental program was to maximize H2 production per mole of O2 supplied (H2(out)/O2(in)). Optimization, using oxygen-to-carbon (O2/C) and water-to-carbon (S/C) ratios as independent variables, was conducted at three pressures using bottled O2. Surface response methodology was employed using a 22 factorial design. Optimal points were validated using H2O2 as both a stored oxidizer and steam source. The optimal experimental conditions for maximizing the moles of H2(out)/O2(in) occurred at a S/C ratio of 3.00–3.35 and an O2/C ratio of 0.44–0.48. When using H2O2 as the oxidizer, the moles of H2(out)/O2(in) increased ≤14%. An equilibrium model was also used to compare experimental and theoretical results.