Spatial patterns and total amounts of soil organic C (SOC) are important data for studies of soil productivity, soil hydraulic properties, and the cycling of C-based greenhouse gases. The study evaluated several approaches for characterizing SOC to determine their relative merits. The first approach entailed grouping data from global pedon SOC database by type of ecosystem, resulting in a total of 78.0 Pg of C to 1-m depth for the contiguous USA. In a second approach, a pedon database was aggregated using soil taxonomy, giving a total for the continguous USA of 80.7 + or - 18.6 Pg of C when the great group SOC was spatially distributed with Major Land Resource Areas (MLRAs) using the 1982 National Resource Inventory (NRI) and the Soil Interpretation Record databases. The third approach used pedon and spatial data from a global soil map grouped by soil unit that resulted in 84.5 Pg of C for the contiguous USA.