Large sets of petroleum fluid data exist for the various reservoir conditions and properties that occur in practice. This book is the result of several years of exhaustive research that gathered data sets from databases all over the world. The data were compared against the results of many published correlations of fluid properties in order to find the "best in class" required in the petroleum industry. Those findings are offered here as recommended use in reservoir engineering calculations. The data sets cover natural gases, reservoir oils, and reservoir waters (brines). The result of this research project is the best correlation for each fluid property. This book will prove to be a valuable resource for reservoir engineers, production engineers who need to determine which set of correlation equations are most useful for their work, and graduate-level reservoir engineering courses.