Methyl tert-butyl ether (MTBE) and ethyl tert-butyl ether (ETBE) are mainly used as additives togasoline in order to enhance the combustion efficiency. As an assignment from the SwedishEnvironmental Protection Agency, IVL has performed a screening study of MTBE and ETBE. Theoverall objective of the screening was to determine concentrations in a variety of media in the Swedishenvironment, in order to judge if the substances are commonly occurring in the Swedish environment.A further aim was to determine key sources and highlight major transport routes.