Compositional modelling of saturated two-phase hydrocarbon reservoirs is a difficult task. When both oil and gas phases are present, the characterization of one phase may not be the same as the other phase, proper characterization will, therefore, become an issue. In this paper, we examine the compositional data of four two-phase hydrocarbon reservoirs. An attempt is made to characterize the reservoir fluids in both the gas cap and the oil column. In addition to the characterization of the plus fractions, we also review reservoir fluid sampling and validation.