A method of determining an air-fuel ratio of an internal combustion engine in real-time includes: calibrating sensitivity of a universal exhaust gas oxygen sensor to a plurality of gases; inputting to a universal exhaust gas oxygen sensor controller a molecular composition of Hydrogen, Carbon, Oxygen, and Nitrogen which comprise a combustion fuel in use in the internal combustion engine; calculating with the universal exhaust gas oxygen sensor controller an air-to-fuel ratio by performing a chemical balance equation calculation based on the universal exhaust gas oxygen sensor sensitivity calibration and the input combustion fuel molecular composition; and transmitting the calculated air-to-fuel ratio to an engine control unit inreal-time.