The stability of seven polycyclic aromatic hydrocarbons (PAHs) were studied in aqueous solutions at 100–350 °C. The aqueous solution of one PAH compound at a time was sealed in a stainless steel bomb-type reaction vessel in an argon atmosphere and heated for 10 to 240 min in an oven. The contents of the vessel were analysed by GC-MS. At 300 °C, degradation was observed even with the shortest heating time, 10 min. The degradation products were typically different oxidation products such as ketones and quinones. In addition to the heating time and temperature, the concentration of the analyte and the inner surface of the vessel affected the results.