In this book, the author presents a detailed complex mathematical and computational model for the simulation of fluid flow in reservoirs. The research was conducted in collaboration with Dr. John M. Tyler of LSU and was funded by the United States Department of Energy. The results were published in a Ph.D. dissertation and at several international conferences. Oil and Gas Reservoirs Hydrocarbons and their associated impurities occur in rock formations that are usually buried thousands of feet or meters below the surface. Scientists and engineers often call rock formations that hold hydrocarbons "reservoirs". Oil does not flow in underground rivers or pool up in subterranean lakes, contrary to what some people think. crude oil and natural gas occur in buried rocks and, once produced from a well, companies have to refine the crude oil and process the natural gas into useful products. Further, not every rock can hold hydrocarbons. To serve as an oil and gas reservoir, rocks have to meet several criteria.