Thermodynamic description and prediction of the complex multi-phase systems, prone to gas hydrate and salt formation, is crucial to the economical and safe design and operation of oil and gas production and transportation facilities, in particular in offshore and deepwater regions. The topics presented in this book included modelling of the phase behaviour and gas solubility in the water-hydrocarbon systems in the presence of electrolyte solutions with/without hydrate organic inhibitors, as well as development of tools and methods to predict gas hydrate formation and salt precipitation problems associated with petroleum exploration and production. A new thermodynamic approach capable of predicting vapour-liquid-solid equilibria (VLSE) in systems containing electrolytes or electrolyte and organic inhibitors at conditions relevant to subsea transportation of oil and gas is presented.Various generic correlation for predicting the hydrate suppression temperature as well as the compatibility concerns of different hydrate and scale inhibitors are also described. Potential of using gas hydrate technology for different processess is also explained.