Abstract The porosity of a reservoir and its water saturation fraction have long been at the heart of wireline and MWD log based formation evaluation. In many formations, however, the complexity of the mineralogy and the properties of the formation's conductivity have only permitted qualitative answers. This has even been true with evaluations based on multi-log data suites. At the 1996 SPE Conference a new NMR logging process, the MRIL®* C/TP system, was introduced. C/TP provides a measure of total porosity independent of mineralogy and dependent only on the hydrogen density of the fluids themselves. This represents a significant advantage over the conventional density, neutron, and acoustic ‘porosity’ logs, which mostly respond to rock properties. Furthermore, the C/TP amplitude can be subdivided into pore size groups associated with clay mineral bound water, capillary bound water and pores free to accumulate hydrocarbon (FFI). Usage of the MRIL has proven the benefit of a borehole-centralized log, a feature that makes it largely independent of borehole size and shape. It has also become recognized as the first porosity log that truly measures the pore system and not some inference of porosity based on the rock matrix. Thus the log analyst is provided with a wireline log that is truly a porosity log which provides a quantitative measure of total and effective porosity. To investigate the accuracy and reliability of these methods and ideas, well bore data are assembled and compared to conventional log and core results. A full description of these comparisons and processes are included to show the benefit of a true porosity measurement that is insensitive to matrix mineralogy and only depend on pore size and fluid contents,the advantage of a porosity measurement largely independent of borehole condition.