Introduction The American Petroleum Institute's (API) Clean Water Issues Task Force (CWITF) commissioned ths report to provide information and guidance to its members on the importance@ presence@ environmental fate@ and analytical methods for cyanide compounds and related chemical species that may be found in petroleum industry wastewater effluents. A principle objective of this report is to provide technical information that will assist NPDES permittees in negotiating site-specific water quality-based effluent limits. The report also provides permittees with guidance on the sampling and analytical methods that must be used to assure that cyanide data are as reliable as practical@ given the limitations of the analytical methods. There are currently no national effluent limitations guidelines for cyanide and related chemicals that are applicable to petroleum industry discharges. However@ the U.S. Environmental Protection Agency (EPA) has adopted water quality criteria for cyanide (EPA@ 1985) under the authority of Section 304(a) of the Clean Water Act (CWA). All of the states and territories have used EPA's criteria@ either directly or with modifications@ to adopt water quality standards for cyanide under the authority of Section 303(c) of the CWA. Because the water quality standards for cyanide are uniformly very low@ and because certain petroleum industry wastewaters contain cyanides@ it is important for API member companies to have information resources that will: (1) assist them in participating in future regulation development by the states; (2) provide technical support for the development of NPDES permit limits@ and (3) provide technical support for determining the levels of treatment required to achieve water quality-based effluent limits (WQBELs) that may be included in NPDES permits. Also@ although this study did not identify in any states any stream segments impaired by cyanide@ there is always the possibility that such a identification could occur and that a total maximum daily load (TMDL) evaluation for cyanide would then be required. The information in this report will be helpful in such cases@ if they were to occur. The chemical functional group cyanide (CN) is found on a number of inorganic and organic compounds. Chemicals containing CN have considerable environmental importance because when CN is present as free. cyanide (hydrocyanic acid (HCN) and the CN- anion)@ it is highly toxic to many life forms. There are several other functional groups that contain the CN structure@ but that generally are much less toxic than CN. These include the thiocyanate (SCN-) group@ the cyanate group (OCN-)@ organic nitriles@ and the selenocyanate group (SeCN-). Because these forms are found in certain petroleum wastes and as degradation products of free cyanide@ they are also discussed in this section.