The fuel adulteration problem is associated with environmental pollution, problems with engine performance, and tax losses. Here, results are presented of a survey in leaded gasoline and automotive diesel, obtained from service stations representative of all the oil companies operating in Greece. For this purpose, 165 samples of gasoline and 420 samples of automotive diesel were collected from various parts of the country during the years 1998, 1999, and 2000. The gasoline samples were subsequently analyzed for their key properties and for any adulteration with cheaper unleaded gasoline. Octane number, benzene, olefins, and total aromatics were determined with the mid-IR method" and the sulfur content with a UVF elemental analyzer; The analysis of the automotive diesel samples concerned some key properties such as the cetane index, density, sulfur content, and the distillation properties of the fuel. The results indicate that there is a large fluctuation of fuel properties among the oil marketers. Examination of the quinizarin content (the tracer of unleaded gasoline) has shown that 11 leaded gasoline samples (8.8%) were mixed with unleaded gasoline, 5 leaded gasoline samples (4%) were mixed with aromatic solvents, whereas about 28% of the automotive diesel samples suffered from some degree of adulteration, mainly with cheaper heating fuel; and one automotive diesel sample was adulterated with a lighter fraction. Fuel misuse is a common problem not only for European countries but for practically every nation in the world. The European Union recently expressed its concern on this issue, mandating that by the year 2002 all the member states will promote the development of a uniform system for fuel quality monitoring.