This industry comprises establishments primarily engaged in (1) manufacturing acyclic (i.e., aliphatic) hydrocarbons such as ethylene, propylene, and butylene made from refined petroleum or liquid hydrocarbons and/or (2) manufacturing cyclic aromatic hydrocarbons such as benzene, toluene, styrene, xylene, ethyl benzene, and cumene made from refined petroleum or liquid hydrocarbons. Cross-References. Establishments primarily engaged in-- ? Manufacturing petrochemicals by refining crude petroleum--are classified in Industry 324110, Petroleum Refineries; ? Manufacturing acetylene--are classified in Industry 325120, Industrial Gas Manufacturing; ? Manufacturing basic organic chemicals (except petrochemicals)--are classified in Industry 32519, Other Basic Organic Chemical Manufacturing; and ? Recovering liquid hydrocarbons from oil and gas field gases--are classified in Industry 21111, Oil and Gas Extraction.