This document gives general guidance for the sampling and gas chromatographic analysis of compressor oil in biomethane or compressed natural gas (CNG). The compressor oil mass fraction is determined by sampling on coalescing filters under defined operational conditions (the two first cubic meters of gas referring to standard conditions, delivered at a refuelling station). Compressor oils are lubricants used in mechanical devices where the purpose is to reduce the volume and increase the pressure of gases for use in a variety of applications. The method is solely applicable to compressed gas (p>18 MPa). The compressor oil content is expressed as mass fraction. The scope of this method is from 3 mg/kg 30 mg/kg.