Nuclear magnetic resonance (NMR) technology from laboratory data and well logs is rapidly gaining acceptance as a petrophysical tool for evaluating reservoir quality. The evaluation of laboratory NMR data as a core analysis technique shows that NMR relaxation time distributions match independent estimates of pore-size distributions. These other pore-size estimates come from grain-size analyses, pore-throat distributions from mercury porosimetry, thin-section petrography, and permeability values. Irreducible water-saturation estimates from NMR-based pore-size distributions also correspond well with independent measures of irreducible water from special core flood tests. In this study, we look at the relaxation time distributions extracted from laboratory and downhole NMR measurements to determine pore geometry and volumetrics within a reservoir. This understanding leads to a better overall reservoir characterization. Both core and log NMR data are used to demonstrate that there is a direct connection between NMR relaxation time distributions and the fundamental property of pore size in sandstones. This description of pore-size distributions allows us to estimate permeability and irreducible water saturation. Additionally, the NMR logs accurately characterize the NMR core (lab) measurements and provide important information that enhances the description of low-resistivity pay.