Partial oxidation of methane to methanol was examined using a new type of reactor tube, single-crystal sapphire, at 10-70 bar, 5-10 mol % O2 in the feed, and residence times from 0.8 to 7.8 min. Both the heated length of the tube and the surface area/volume were kept relatively small in comparison to some past studies. Methanol selectivities of ca. 70% at C1/O2 = 14.3 (C1/air = 3) and 55-60% at C1/O2 = 5.7 (C1/air = 1.2) were attained at 100% O2 conversion. At 100% O2 conversion, reactor residence time and temperature profile (e.g., reactor quench cooling, feed preheating) appeared to have little effect on CH3OH selectivities. Longer residence times can increase methane conversion at constant temperature until 100% O2 conversion is reached. The addition Of CO2 to increase total pressure favorably affects both selectivity and conversion. These results are compared to previous work on low-temperature, homogeneous methane oxidation; differences are explained in terms of different reactor geometries and reactor surfaces and the effects of total pressure on elementary radical reactions.