In November 2003, Acting Deputy Administrator Stephen L. Johnson requested an internal review of the Superfund program (the "120-Day Study") to identify opportunities to achieve program efficiencies that would enable EPA to begin and complete more long-term cleanups with existing program resources. One of the recommendations resulting from that review was to evaluate regional PRP search programs to identify practices indicative of enforcement success and barriers to achieving it. In response to this recommendation, the Office of Site Remediation Enforcement (OSRE) undertook a PRP search evaluation in consultation with the National PRP Search Enhancement Team. Four main data points were used for benchmarking analyses: PRP determinations, PRP search costs, EPA response costs, and PRP response costs. OSRE relied primarily on IFMS data to determine total EPA response costs and PRP search costs and primarily on CERCLIS data for PRP determinations and PRP response costs. PRP search costs and EPA response costs include direct and estimated indirect costs. Each data point was updated during the study. Preliminary analysis indicated that site groups with the greatest variability in total search costs and CPD were owner/operator sites, waste contributor sites, and sites with de minimis parties. Data analysis therefore focused on these groups. In addition, OSRE surveyed EPA's regions to identify PRP search practices and barriers to effective and efficient PRP searches and to identify additional variables that might explain regional CPD differences. Results of the data analysis and survey demonstrate that the uniqueness of each PRP search is the major challenge to evaluating the effectiveness and efficiency of search activities and to identifying PRP search practices and barriers to success. Even among sites categorized by type, each has unique characteristics that affect the conduct of the PRP search. Each PRP search presents its own obstacles and each regional program adapts its own unique practices and procedures to overcome them as they arise. In this study, EPA collected information on regional PRP search organizational and operational characteristics to determine if there was any correlation between the outcomes of the site-specific analyses and regional program characteristics. Responses to the survey were not sufficiently consistent to compare to site-specific data, but they provided certain insights into the operation of regional PRP search programs: Whether regions use separate organizational units for PRP search functions depends on the size of the region; Whether regions dedicate specific job classifications to PRP search functions depends on the size of the region; Regions organize site-specific case teams to perform PRP search functions. Most regions have contract vehicles in place to obtain extramural support in performing PRP search functions; Regions tend to use contractor support either for skilled research and technical tasks generally required on an ad hoc basis or on routine and less skilled clerical and data management tasks; Regions charge outlays for contractor support site-specifically and concentrate them on case development and legal and financial analysis; Regions charge FTEs allocated for PRP search-related tasks site-specifically and use them primarily for case development and legal analysis and documentation tasks; Regions allocate funds available for PRP search-related activities on the basis of site-specific factors; Regions develop site-specific plans for conducting PRP searches. Regions initiate PRP search activity, e.g., a deed search for the current owner, during the preliminary assessment/site investigation (PA/SI) stage or at the earliest appropriate time before the site is proposed for the NPL.