The Stage 1 Disinfectants/Disinfection Byproducts Rule requires analyses of total organic carbon (TOC) in drinking water sources. In this study, water samples from 102 watersheds across North America were used to compare three TOC methodologies. All analyses were performed on filtered samples, eliminating particles and permitting a foucs on the dissolved organic carbon (DOC) constituents. High-temperature combustion yielded significantly lower DOC concentration estimates than methods based on either wet chemical oxidation (9 percent difference) or ultraviolet-promoted oxidation (10.5 percent difference). All three methodologies gave similar concentration estimates (no significant differences) after correction for a pH-dependent loss of nonvolatile DOC during the external sparging of samples to remove inorganic carbon. The author concludes that current TOC technologies are capable of providing accurate and equivalent estimates of DOC concentrations; nonetheless, he contends that appropriate dissolved and particulate performance standards for TOC analyses would constitute an important tool for analysts in the drinking water industry. Includes 17 references, table, figures.