Numerical geologic models are built for many purposes. Models at a cubic-millimeter resolution are required to understand how small-scale heterogeneity observed in core photographs and image logs affects vertical permeability. Models at 1 dm³ (0.001 m³) resolution are required to understand the variability of properties within the grid blocks that will be used in the flow simulator. Models at a 1000 m³ (3531 ft³) resolution are required to understand the variability between grid blocks to model specific recovery processes. Models at the 10¹² m³ (3.53 10¹³ ft³) scale are required to assess resources over large areas. No single numerical geologic model is fit for all purposes. Many of the same tools are used at different scales, but notable differences related to the use of categorical and/or continuous variables, the number of variables, and conditioning to different data types exist. Three important model types and the implemented choices are described: (1) large-scale multivariate mapping for resource and/or reserve assessment, (2) reservoir-scale three-dimensional (3-D) modeling for reservoir development planning, and (3) high-resolution modeling to understand effective flow parameters at the flow-simulation scale.