Ethanethiol (EtSH) is an organic compound with the formula CH3CH2SH. It consists of an ethyl group, CH3CH2, attached to a thiol group, SH. Its structure parallels that of ethanol, but with S instead of O. The presence of S leads to many different properties, most notably the infamous odour of EtSH. Ethanethiol is also more volatile than ethanol due to a diminished ability to engage in hydrogen bonding. Ethanethiol is toxic. It occurs naturally as a minor component of petroleum, and may be added to otherwise odourless gas products such asliquefied petroleum gas (LPG) to help warn of gas leaks. At these concentrations, ethanethiol is not harmful.