This demonstration test successfully demonstrated the operation of a commercial phosphoric acid fuel cell (FC) on landfill gas (LG) at the Penrose Power Station in Sun Valley, CA. Demonstration output included operation up to 137 kW; 37.1% efficiency at 120 kW; exceptionally low secondary emissions (dry gas, 15% O-2) of 0.77 ppmV CO, 0.12 ppmV NOx, and undetectable SO2; no forced outages with an adjusted availability of 98.5%; and a total of 707 h of operation on LG. The LG pretreatment unit (GPU) operated for a total of 2297 h, including the 707 h with the FC, and documented total sulfur and halide removal to much lower than the specified < 3 ppmV for the FC. The GPU flare safely disposed of the removed LG contaminants by achieving destruction efficiencies greater than 99%.