An HPLC technique for separating and identifying phenolic compounds in aqueous samples is established. The same technique is applied to non-aqueous samples (coal liquids, petroleum, shale oils, etc.) after first isolating a polar fraction containing the phenolics by means of a silica Sep-Pak®. Thirty eight phenolic model compounds were separated and response factors established. Several HPLC reverse-phase columns were evaluated during the development of this technique, which included 5µ and 10μ-particle sizes for both C8 and C18 columns. These conventionally packed columns were compared with a radially compressed column; a wide variety of gradients was employed.