a nitrogen - rich inert gas mixture is produced by the partial oxidation of a hydrocarbonaceous feed containing substantially no metals nor noncombustible materials with air in a free - flow , unpacked , refractory - lined gas generator at a temperature in the range of about 1300 ° to 3000 ° f . and a pressure in the range of about 1 to 250 atmospheres . the product gas will comprise a mixture of nitrogen , argon and carbon dioxide and may contain small amounts of hydrogen and carbon monoxide , depending on the o / c atomic ratio selected . the atomic ratio of free oxygen in said air to carbon in said hydrocarbonaceous fuel is in the range of about 1 . 7 to stoichiometric , or slightly less than stoichiometric . by operating at this level of o / c atomic ratio , the h 2 + co content of the product gas may be minimized or deleted , substantially all of the particulate carbon may be oxidized , substantially no no x is produced , and the product gas contains substantially no free oxygen . further , the sensible heat recovered from the product gas may be used to manufacture by - product high pressure steam for export . the nitrogen - rich product gas may be used for oil formation flooding , or as a pressurizing or blanketing gas . costly gas compressors may be avoided since the product gas may be produced at or above use pressure .