Disclosed are methods, systems, and computer-readable mediums for determining the composition of gaseous fuel. An initial gaseous fuel stream is provided that includes methane, non-methane hydrocarbons, and inert gases. Air is mixed into the initial fuel stream upstream of a first catalyst. The first catalyst oxidizes only the non-methane hydrocarbons of the initial fuel stream to produce a resultant fuel stream comprising methane and inert gases. Air is mixed into the resultant fuel stream downstream of the first catalyst and upstream of a second catalyst. The second catalyst oxidizes only the methane hydrocarbons of the resultant fuel stream to produce an output fuel stream. Mole ratios of the methane, the non-methane hydrocarbons, and the inert gases of the initial fuel stream are each determined.