A 2002 mercury emissions inventory developed by the Northeast States for Coordinated Air Use Management using standard fuel oil mercury (Hg) emission factors from the U.S. Environmental Protection Agency (known as US EPA "AP-42" factors) identified residential fuel oil combustion as an important contributor to Hg air emissions in the northeastern United States. Published literature values, however, suggest much lower mercury content in heating oil than inferred from the US EPA factors. To better characterize mercury (along with other trace element) content in heating oil sold in the Northeast, we conducted a two-phase sampling and analysis study of commercially available fuel oil sold in the northeastern U.S., with a focus on New York State. Changes between the two study periods and relationships between trace element and sulfur levels were evaluated. The study found that concentrations of mercury and other trace elements sampled during both study phases were within typical ranges reported in the literature. Although the average sulfur level in the samples dropped by 2 orders of magnitude between the two phases because of new government regulations limiting sulfur content in fuel oil after the first sampling phase, we observed no significant relationship between sulfur content and the other trace elements. In addition, derived emission factors for almost all trace elements showed lower values than the tabulated US EPA AP-42 factors. The lower mercury content measured in the samples indicate that heating oil combustion is a much lower source of mercury emitted to the air in the northeastern U.S. than would be inferred from an emission inventory developed using US EPA emission factors.