Polycyclic aromatic hydrocarbon (PAH) partitioning coefficients between sediment organic carbon and water (KOC) values were determined using 114 historically contaminated and background sediments collected from eight different rural and urban waterways in the northeastern United States. More than 2,100 individual KC values were measured in quadruplicate for PAHs ranging from two to six rings, along with the first reported KOC values for alkyl PAHs included in the U.S. Environmental Protection Agency's (U.S. EPA) sediment narcosis model for the prediction of PAH toxicity to benthic organisms. Sediment PAH concentrations ranged from 0.2 to 8,600 μg/g (U.S. EPA 16 parent PAHs), but no observable trends in KOC values with concentration were observed for any of the individual PAHs. Literature KOC values that are commonly used for environmental modeling are similar to the lowest measured values for a particular PAH, with actual measured values typically ranging up to two orders of magnitude higher for both background and contaminated sediments. For example, the median log KOC values we determined for naphthalene, pyrene, and benzo[a]pyrene were 4.3, 5.8, and 6.7, respectively, compared to typical literature KOC values for the same PAHs of 2.9, 4.8, and 5.8, respectively. Our results clearly demonstrate that the common practice of using PAH KOC values derived from spiked sediments and modeled values based on n-octanol–water coefficients can greatly overestimate the actual partitioning of PAHs into water from field sediments.