The closed-loop threeway catalyst on the European market has considerably reduced the emissions of passenger cars in an absolute sense. The question arose if gaseous fuels still have a real advantage. To answer this question an extensive programme was set up to compare gasoline and diesel with LPG and natural gas. Not only the regulated components, but also a whole range of unregulated components were measured. The resulting data were grouped into environmental aspects, such as direct local toxicity, longterm toxicity, smog, acidification and global warming. The conclusion is that gaseous fuels still hold an advantage over liquid fuels.