WASHINGTON - Government officials handling billions of dollars in oil royalties partied, had sex with and accepted golf and ski outings from employees of energy companies they were dealing with, federal investigators said Wednesday.

The alleged transgressions involve 13 former and current Interior Department employees in Denver and Washington. Their alleged improprieties include rigging contracts, working part-time as private oil consultants, and having sexual relationships with - and accepting golf and ski trips and dinners from - oil company employees, according to three reports released Wednesday by the Interior Department’s inspector general.

The investigations reveal a “culture of substance abuse and promiscuity” by a small group of individuals “wholly lacking in acceptance of or adherence to government ethical standards,” wrote Inspector General Earl E. Devaney, whose office spent more than two years and $5.3 million on the investigation.

“Sexual relationships with prohibited sources cannot, by definition, be arms-length,” Devaney said.

MMS Director Randall Luthi, in an interview with the AP, said the agency was taking the report “extremely seriously” and would review the allegations and weigh taking appropriate action in coming months.