Within a cooperative SHELL-PORSCHE research project the effects of gasoline formulation on emission of regulated and unregulated exhaust gas components and engine performance have been investigated. Both unconventional fuels composed from refinery components and special blends from pure chemicals have been tested on a single cylinder research engine and a 4-cylinder production engine under controlled conditions. CO2-emissions were found to be strongly dependent on fuel carbon content. T90 distillation point has a strong effect on total hydrocarbon emissions. Aromatics content in the fuel is the dominating factor on emission of aromatic hydrocarbons. Aldehyde emissions increased with decreasing aromatic content in the fuel. Oxygenated fuels gave relatively low NOx-emissions. Methane showed very favourable results with respect to all exhaust gas components investigated. With the liquid fuels no effect of fuel composition on engine performance was found.