AbstractA number of methods of synthesis of methanol labelled with 18O or with 17O have been evaluated. The best method is considered to be the partial hydrolysis of trimethyl phosphate. Ethanol‐18O can be prepared analogously by the partial hydrolysis of triethyl phosphate. The most accurate method for the isotopic analysis of oxygen in methanol is by pyrolysis in a specially designed vessel, the hydrogen being extracted through a palladium tube and the residual carbon monoxide analysed mass‐spectrometrically.