Electro-discharge machining (EDM) is a nonstandard electro-thermal machining technology used to produce geometrically complex or hard material parts that are highly challenging-to-machine by traditional machining methods. By igniting quick and repeating spark discharges between the tool and work piece separated by a narrow gap of around 0.01 to 0.50 mm, the method allows for the controlled erosion of electrically conductive materials. This void is filled with a dielectric fluid, either by flooding or immersion. The goal of this study is to evaluate the optimal process parameters of Argon gas assisted machining on P91 steel super alloy material with copper as a tool electrode and kerosene as a dielectric fluid. Experiments were carried out to determine the link between the current pulse on and off times, as well as the material removal rate and tool wear rate. EDM in gas is recent modification in machining method. In this method, EDM is performed with gas and kerosene-based oil, so that pollution reduces. The greatest advantage of EDM in gas is very low level of electrode wear rate.