A method for treating a crude natural gas feed stream comprising methane and having a first carbon dioxide concentration, said method comprising the steps of: subjecting the crude natural gas feed stream to a separation process to provide: a purified natural gas stream having a second carbon dioxide content which is lower than the first carbon dioxide concentration in said crude natural gas stream; and, a carbon dioxide stream comprising carbon dioxide as the major component and methane; recovering the purified natural gas steam; optionally mixing the carbon dioxide stream with make-up methane and/or make-up air; passing the carbon dioxide stream and optional make-up methane or air through a heat exchanger to raise the temperature of the stream to the desired inlet temperature T1 of an oxidation reactor; optionally mixing the carbon dioxide stream with make-up methane and/or make-up air; passing the heated stream from step (d) and any optional make-up methane and/or air to the oxidation reactor containing an oxidation catalyst, where the methane is oxidised; removing a gas stream including the products of the oxidation reaction from the reactor, said gas stream being at an outlet temperature T2 which is higher than the inlet temperature T1; passing the gas stream removed in step (g) through the heat exchanger against the carbon dioxide stream from step (a) to allow the heat to be recovered from the gas stream removed in step (g) and utilised to heat the carbon dioxide stream in step (d); and measuring the outlet temperature T2 and controlling the inlet temperature T1 by adjusting the amount of make-up methane and/or air added in step (c) and/or step (e).