N2 content is reduced by using relatively pure O2 in the synthesis gas production. The O2 and CH4 are separately preheated to 1,000° F. Then direct partial combustion takes place under a pressure of 200-300 p. s. i., temperature at least 2,200° F. by using 10% excess O2 in combustion step a synthesis gas is produced, 90-95% H2:CO=1.8:1-2.1. The remainder is unconverted CH4 and CO2. If the CO content of the gas charged to the synthesis step is properly limited, the catalyst does not become defluidized. The limiting is done by mixing inert gas diluents such as tail gas with the make gas. The total gas charged at the base of the reactor should contain less than 15 mol. %, preferably not more than 12 mo. % of CO during normal operation. The H2:CO:CO2 ratio in the reactor charge should be approximately 3:1:2 and a Z number 3-9, where Z is the quotient of mol. % H2 multiplied by mol. % CO2 and divided by the square of the mol. % CO. 11 United States patents cited.