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Substances & Categories

Petroleum (crude oil) and raw natural gas and condensates are naturally occurring substances potentially containing thousands of individual chemicals called hydrocarbons. After crude oil is removed from the ground, it is sent to a refinery by pipeline, ship, or barge. In order to make finished petroleum products, these substances are separated at the refinery into different boiling fractions (i.e., gases, naphtha, residuum, etc.). Each of these fractions typically requires additional processing before they can be sold or blended into finished petroleum products like gasoline, diesel fuel, motor oil, etc.

The separated fractions are often referred to as “petroleum process streams” and are individual substances defined according to the last processing step that they have undergone. Petroleum substances are subject to nomenclature rules developed jointly by the United States Environmental Protection Agency (EPA) and the American Petroleum Institute (API); this nomenclature used is presented in API’s published reference document, “Petroleum Stream Terms Included in the Chemical Substance Inventory for the Toxic Substances Control Act (TSCA)”. The Stream Terms defined in this document include the Chemical Abstract Services (CAS) registry number, name, and definition. A substance entry in this document typically contains the following information:

  1. The primary fraction such as Gases, Naphtha, Distillate/Gas Oil, or Residuum. Other nomenclature such as Extracts, Wax, etc. may be used for specific refinery processes.
  2. The hydrocarbon source.
  3. The last refining step.
  4. The carbon number range.
  5. The boiling point range.

An example provided below shows the substance definition for heavy catalytic cracked distillates, with the information in the numbered listed above annotated in superscript:

CAS Number; 64741-61-3

CAS Name; Distillates1 (petroleum2), heavy catalytic cracked3

CAS Definition; A complex combination of hydrocarbons produced by the distillation of products from a catalytic cracking process. It consists of hydrocarbons having carbon numbers predominantly in the range of C15 through C35 4 and boiling in the range of approximately 260 °C to 500°C (500°F to 932°F) 5. This stream is likely to contain 5 wt. % or more of 4- to 6- membered condensed ring aromatic hydrocarbons.

A full list of the petroleum substances sponsored in the HPV Challenge Program can be found here.

HPV Categories

The petroleum substances described above are often organized and evaluated according to product categories. Grouping substances into categories based on expected similarities in hazard information for human and ecological receptors is a useful tool for summarizing the existing data and for addressing potential data needs/data gaps. Because categorizing substances requires all existing data for each substance to be compiled, this process also helps to avoid unnecessary duplication of testing. Categories are typically organized around properties and refinery processes such as similar boiling ranges, similar process history, or similar end-uses. Categories are fit-for-purpose depending on the regulatory or industry sector requirements.The petroleum HPV product categories are:


In addition to the HPV petroleum categories, many petroleum substances have also been categorized for the European Community Regulation on chemicals and their safe use; hazard information on these substances is compiled under the Registration, Evaluation, Authorization and Restriction of Chemicals (REACH) regulatory program in the form of dossiers accessible through an online database. Under REACH regulation, manufacturers and importers are required to gather information on general properties and hazards of their chemical substances, and to register the information in a central database run by the European Chemicals Agency (ECHA). A comparison of the petroleum categories used for the EPA’s HPV Challenge Program and the petroleum categories used for REACH registration in Europe (circa 2010) can be found here.

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