The continuing growth in the importance of oil and gas production and processing overall the globe increase the need for accurate prediction of various parameters and their impact on unit operations, process simulation and design. Because of the particular nature of various parameters, sometimes existing methods encounter difficulties. Currently several models are available to predict various design parameters in the oil and gas processing industries. However, their calculations may require rigorous computer solutions. Therefore, developing the new predictive tools, which are easier than the existing methods, less complicated with fewer computations to minimize the complex and time- consuming calculation steps is an essential need. It is apparent that mathematically compact, simple, and reasonably accurate predictive tools, as proposed in this thesis, would be preferable for computationally intensive simulations. This problem has been circumvented conveniently by resorting to simpler approaches, as described in this book.