BTEX is a collective term for the highly volatile aromatic hydrocarbons benzene, toluene, ethylbenzene and xylenes. The BTEX aromatics are, among other things, a component of fuels (to increase the octane rating) and are used as solvents and degreasing agents. The single compound benzene is classified as carcinogenic. Due to their high volatility and high mobility (similar to that of CHC), BTEX aromatics can easily spread in soil and groundwater and accumulate in the soil air. However, they have a lower density than water and therefore do not sink into the groundwater body.