An industrial anthracene oil (AO) was polymerized by thermal treatment with the aid of AlCl 3, sulphur and air. The composition of the reaction products was investigated by size exclusion chromatography (SEC) and synchronous UV-fluorescence spectroscopy. The SEC profiles show significant differences in the composition of the polymerized products. This suggests that the reactivity of the AO components and the mechanisms of polymerization are different. With sulphur and air, the polymerization involves a low number of AO components, which selectively react to form intermediate and large polymers. AlCl 3 causes a more extensive polymerization, giving rise to a product in which the fraction of oligomers of intermediate size (500–700 u) is predominant. Synchronous UV-fluorescence spectroscopy corroborates and supports the SEC results.