Because of the complex character of petroleum fractions and products, gas chromatography plays an important role as an analytical technique in this area. For the majority of oil fractions classifying or group-type analyses are performed rather than determinations of all the individual constituents. The general composition of petroleum is discussed and also the relation between composition, product properties and processability. Compositional analyses for petroleum products are reviewed, especially in terms of multi-dimensional gas chromatography. The important role that comprehensive two-dimensional gas chromatography is expected to play in the near future in unraveling the composition of oil fractions is also discussed.