A mercury-catalyzed system using H2SO4-SO3 as the reaction medium for the oxidation of methane to methanol has been studied in the temperature range 150-200 degreesC at methane pressure from 40 bar to 100 bar. Systematic experimental designs were applied to study the effect of temperature, gas pressure, catalyst amount, reaction rate, and liquid agitation speed. The experiments were performed in a high-pressure reactor. The system for the catalytic conversion of methane to methanol using HgSO4 as catalyst is a very efficient process. Analyzing the pressure-time relationship of the reaction gives well-defined information about the reaction rate and indicates a one-to-one reaction between HgSO4 and methane. The pressure drops after the reaction equilibrium is reached are the same independent of catalyst amount. Higher reaction temperature and pressure lead to higher reaction rate. The effect of adding HgSO4 stops when the solubility of HgSO4 in the reaction media is reached. (C) 2000 Academic Press.