This Technical Report (TR) provides guidance and a methodology for determination of carbon content from hydrocarbon-based petroleum and petrochemical products@ and the uncertainty of the average carbon content as calculated from multiple samples taken during a reporting period. This method is intended to make use of industryaccepted mixture property data and test methods with no new or modified test methods introduced in this document. The method is applicable to carbon-content-based reporting or trading for all gaseous and liquid hydrocarbons. This TR provides references and supplemental information on applicable industry practices based on the published resources@ existing industry standards@ industry-accepted physical constants or properties of hydrocarbons for measurement@ sampling@ sampling frequency@ and analysis of hydrocarbon samples.