Noncatalytic direct oxidation of methane was conducted in a high pressure flow type system to clarify the effect of operational factors and additives. The reaction conditions were 300-500-degrees-C; 21-41 atm; CH4/air ratio, 3/1-17/1; residence time, 3-15 s. Methanol selectivity was affected by reaction conditions, especially the methane/oxygen ratio. Additives such as carbondioxide, hydrogen, and hydrocarbons improved methanol selectivity and reduced the initiation temperature of the methane-oxygen reaction. The observations suggest that hydrogen-donating species may be essential for selective methanol formation.