Modern depositional settings provide unambiguous geomorphic data facilitating the quantification of geologic interpretations for the numerical characterization of subsurface strata. Traditional three-dimensional geologic descriptions are limited by one- and two-dimensional data sources: generally well and outcrop data. However, geomorphic analyses of fluviodeltaic systems yield size distributions for discrete sedimentary units. These distributions provide constraints for conditioning the area (X and Y dimensions), shape, placement, and preferred orientation(s) of sedimentary units in reservoir models. Dimensional data for channel belts, channels, channel bars, crevasse splays, distributary channels, and distributary mouth bars from the fluvially dominated deltas of the Alaska North Slope and the Louisiana Gulf Coast reveal log-normal distributions for their lengths and widths. Modern analogs provide statistical constraints for conditioning data input for geologic facies associations in object-based reservoir models. Geomorphic data from modern fluviodeltaic analogs are linked with core and wire-line-log data to render conditioned, three-dimensional geologic models. Model accuracy relies on bed thickness and chronostratigraphic constraints imposed by cores and stratigraphic correlations, as well as the lateral extent of facies associations governed by geomorphology. These object-based reservoir models demonstrate the impact that varying the population of lengths and widths for geologic features has on sand body distribution and interwell continuity.