A process for measuring methane emissions by an internal combustion engine includes connecting a methane sensor to an exhaust line of the internal combustion engine such that a portion of the gas in the exhaust line can enter the methane sensor, operating the internal combustion engine so as to produce the exhaust, measuring a methane concentration of the gas from the portion of the gas from the exhaust line with the methane sensor, and producing an output from the methane sensor corresponding to the methane concentration. The methane sensor is plumbed to the exhaust line. The methane concentration is continuously sampled by the methane sensor. The methane sensor can be an electrochemical cell, a catalytic methane sensor, or an infrared methane sensor.