Barks From Four common Mediterranean trees subjected to phenolysis under acidic conditions at moderate temperature 130degreesC or 150degreesC) were evaluated with pyrolysis-molecular beam mass spectrometer (py-MBMS). The results indicated that both concentration of acid catalyst and the phenolysis temperature have an impact on the chemical composition of both the isolated oils and the solid residue, with the acid concentration having the greatest influence. The primary phenolysis reaction products included phenolics and Furans. As expected, at higher acid concentrations the phenolysis products contained less carbohydrate and included more phenolic fragments. These phenolysis oils should be useful as feedstocks for the production of phenol formaldehyde resins. The py-MBMS method was found to be an effective and convenient method to understand bark phenolysis. Published by Elsevier Science Ltd.