Onshore Processing Facilities is one of the industries engaged in natural gas processing. The total use of natural gas over the last four years tends to increase. OPF also utilizes electrical energy as secondary energy generated from GEG. Currently the condition of installed equipment such as GEG, air compressor, HVAC, and building lighting is 8 years old, so there are indications of a decrease in efficiency. Then the GEG condition which only generates electricity around 30% of its capacity is also suspected to cause low engine efficiency. Therefore, it is necessary to conduct an energy audit to determine energy use and potential savings that can be made. Based on an audit conducted by the SEC for 2022, 0.8 GJ/TOE is still relatively efficient. The Air Compressor System has an average efficiency of 78.73%, the HVAC unit has a COP value of 3.31, the lighting level of each room in the OPF building does not meet the minimum standard, which is around 125 - 450 lux, and GEG has an efficiency value of 27.2 %, which is below the design standard. Opportunities for savings that can be made are by reducing the compressor air pressure by 0.7 bar can save Rp. 21,778,565, installing a capacitor bank of 416 micro farads in the HVAC system can increase the value of cos phi to 0.95, replacing building lights with 28 watts installed recess type 69 units to meet lighting standards, and the use of PLN electricity will save electricity costs of IDR 2,367,557,200.