Bioethanol, as defined by the U.S. Department of Energy, is a renewable fuel made from biomasses. It has widespread use in producing gasohol, a blend of alcohol and gasoline, which is utilized as an alternative fuel for cars and other vehicles in various countries. As part of Thailand’s effort in fighting pollution and climate change, there is a gradual national effort to shift the usage of gasoline to gasohol. Volatile congeners, such as C3-C5 mono-alcohols, are undesirable production by-products that can be present within the biofuel. To safeguard consumer confidence, the Thai government has developed regulatory guidelines to ensure the composition and quality of ethanol fuel products. In this application note, a method utilizing a PerkinElmer Clarus® 590 GC/FID for the analysis of samples in support of the Thailand Industrial Standard is presented.