The U.S. Interior Department has disciplined more than a half-dozen workers who accepted lavish gifts, partied and in some cases had sex with employees from the energy companies they regulated.

The actions announced Friday range from a warning letter to termination. The Interior Department would not confirm how many employees were fired, citing privacy.

The eight employees at one time worked in a Denver Minerals Management Service office in charge of collecting billions of dollars in federal oil royalties.

An Interior Department Inspector General investigation issued in September referred to a "culture of substance abuse and promiscuity" in the office from 2002 through 2006. During that time, the report found that some employees were getting drunk and having sex with oil company personnel. The report also highlights instances where co-workers in the office used cocaine and marijuana.

Much more widespread were the golf and ski trips, snowboarding lessons and concert tickets workers in the office accepted from oil companies. Nearly a third of the 55-person staff in the Denver office had accepted gifts, but only nine workers had exceeded the $20-per-gift limit or $50-a-year threshold on outside gifts.

Minerals Management Service Director Randall Luthi said in a statement Friday that "the behavior of some MMS employees prior to 2007 was clearly inappropriate and warranted strong administrative action."

Eight of those workers were still employed with the agency when the scandal broke, but not in the same office.

Interior Secretary Dirk Kempthorne had vowed to act swiftly to squelch what he called an "ethics storm." Disciplinary procedures for civil servants prevented him from taking action for at least a month.