INTRODUCTION BACKGROUND Since 1987@ the American Petroleum Institute (API) has funded efforts to establish reliable analytical laboratory methods for the measurement of a wide range of petroleum hydrocarbons in soil. Currently available methods@ although many are approved by the U.S. Environmental Protection Agency (EPA) and are in wide use by laboratories@ are generally limited to certain analytes and/or are lacking in rigorous method performance data. For example@ many total petroleum hydrocarbon (TPH) tests use Freon-113?@ which is not effective in extracting heavy distillates. TPH tests also have low recoveries for volatile hydrocarbon components of gasoline. Results from analyte-specific methods@ such as EPA's SW-846 methods and 600 series@ are difficult to correlate to particular petroleum products. As a consequence@ API sought to develop improved methods for gasoline-range and diesel-range organics in soil. API conducted a literature search and symposium to identify an analytical procedure for gasoline-range organics@ originally defined as hydrocarbons in the Ce-C1o range@ at environmental (ppb or ppm) concentrations. The selected method was to rely on existing technology and consider regulatory guidelines. The method selected was a capillary column gas chromatography/flame ionization detector (GC/FID) technique@ with sample introduction by extraction in methanol followed by purge-and-trap. A single laboratory validation study was conducted@ as well as an evaluation of sampling techniques. The initial draft of the GRO method@ the results of the single laboratory validation study@ and the evaluation of sampling techniques are presented in Enseco (1991). The inter-laboratory study presented in this report is a continuation of the GRO research reported in Enseco (1991). Since that study@ two additional methods - a diesel-range organics (ORO) method to measure C10-C28 hydrocarbons@ and a petroleum hydrocarbons (PHC) method to measure C10-C28 hydrocarbons - have been drafted and are also addressed by this inter-laboratory validation study. The GRO and DRO methods were developed by API@ and the PHC method was developed by Shell Development Company.