A method and system of providing compressed substantially oxygen-free exhaust gas for industrial purposes including the steps of extracting exhaust gas from a lean burn engine consuming a mixture of natural gas fuel and air, passing the extracted exhaust gas through a cooling step to cause entrained water vapor therein to condense out, separating and disposing of the condensed water, measuring the oxygen content of the exhaust gas, using the measurement to regulate the quantity of natural gas fed into an igniter into which the exhaust gas is also fed so that substantially all of the oxygen in the exhaust gas is consumed by combustion with the natural gas in the igniter to provide at an outlet of the igniter substantially oxygen-free exhaust gas, and compressing the substantially oxygen-free exhaust gas to provide compressed exhaust gas for industrial applications.