The objective of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) as amended by the Superfund Amendments and Reauthorization Act (SARA) is to reduce and eliminate threats to human health and the environment posed by uncontrolled hazardous waste sites. To meet this objective, CERCLA created: a hazardous waste site response program; and a comprehensive liability scheme that authorizes the government to hold persons who caused or contributed to the release of hazardous substances liable for the cost or performance of cleanups. CERCLA provides EPA with three basic options for cleaning up a hazardous waste site: Under CERCLA Sections 104 and 107, EPA can perform a response action at the site using Superfund money and recover response costs from potentially responsible parties (PRPs). Under CERCLA Section 106, EPA can order, or ask a court to order, PRPs to clean up the site. Under CERCLA Section 122, EPA can enter into settlement agreements with PRPs that require PRPs to clean up the site or reimburse the United States for cleanup under CERCLA Section 107.A PRP search seeks to establish evidence of liability by identifying PRPs and associating their waste type and volume with that found at the site. EPA identifies PRPs and collects evidence by collecting site documents, performing title searches, sending Section 104(e) information request letters, reviewing documents, conducting interviews, and performing research. The information gathered during a PRP search should enable EPA to assess the nature of the party's potential liability at the site. The PRP search should gather information about a party=s potential defenses (e.g., third party defense, divisibility) or exemptions (e.g., municipal solid waste, Superfund Recycling Equity Act). In addition, the PRP search should identify those PRPs that may have a limited ability to pay (ATP) or are insolvent or defunct. Finally, the PRP search should assist in the early identification of contributors of relatively small quantities of hazardous substances (e.g., de minimis and "de micromis" parties). One of the primary objectives of the PRP search is to identify the entire universe of PRPs. Thorough PRP searches enhance EPA's success in negotiating with PRPs to conduct the response activity under EPA's oversight. In addition, early identification of PRPs enables EPA to issue general notice letters (GNLs) promptly to parties to inform them of their potential liability at a site. These PRPs may then be able to help EPA locate other PRPs to share the cost of the response activity. When PRPs are identified and notified early in the remedial process, there is a greater likelihood that they will decide to undertake appropriate response actions. Finally, the early identification of PRPs affords EPA the opportunity to settle with small volume contributors promptly, thereby minimizing their transaction costs.