[en] On July 1, 1993, a Regulatory Oversight (RO) organization was established within the United States Department of Energy (DOE), Oak Ridge Operations (ORO) to provide regulatory oversight of the DOE uranium enrichment facilities leased to the United States Enrichment Corporation (USEC). The purpose of the RO program was to ensure continued plant safety, safeguards and security while the Paducah and Portsmouth gaseous diffusion plants (GDPs) transitioned to regulatory oversight by the Nuclear Regulatory Commission (NRC). These activities were performed under the authority of the lease agreement between DOE and USEC until NRC issued a Certificate of Compliance or approved a Compliance Plan pursuant to Section 1701 of the Atomic Energy Act of 1954, as amended, and assumed regulatory responsibility. This report chronicles the formal development, operation and key activities of the RO organization from its beginning in July 1993, until the turnover of the regulatory oversight responsibility to the NRC on March 3, 1997. Through its evolution to closure, the RO program was a formal, proceduralized effort designed to provide consistent regulation and to facilitate transition to NRC. The RO Program was also a first-of-a-kind program for DOE. The process, experience, and lessons learned summarized herein should be useful as a model for transition of other DOE facilities to privatization or external regulation