Accurate information on phase behaviour and properties of fluids is an essential element in proper management of petroleum reservoirs. Reservoirs were often produced by depletion in which the reservoir pressure was the main variable that controlled the fluid properties. Hence, experimental methods and predictive correlations with pressure as the variable were developed and successfully used for many years in industry. The development of enhanced oil recovery techniques and growing interest in gas condensate and volatile oil reservoirs, involving wide compositional variations and complex fluid behaviour during production, necessitated the use of more advanced compositional methods and new experimental procedures. The availability if high computational capabilities greatly assisted the rapid technology development in this area and its wide use in industry. This book covers the recent advances in a classical manner as a continuation of the conventional technology known as the PVT analysis of petroleum reservoir fluids.