Abstract: There are provided systems and methods for using fuel rich partial oxidation to produce an end product from waste gases, such as flare gas. Lambda sensor modifications and other control parameters that provide closed-loop mixture control at extremely fuel-rich operating conditions utilizing feed-forward and feedback approaches, physics-based engine models, novel use of a lambda sensor (O2-based sensor), sensors with intermittent contact with the gas stream. In an embodiment the system and method use air-breathing engines having control systems, control parameters, sensors and input/output (I/O) for the fuel rich (ER of 1.2 and greater), partial oxidation of the flare gas to form syngas. In embodiments the syngas is further converted into an end product. In an embodiment the end product is methanol.