WASHINGTON — Interior Secretary Dirk Kempthorne told Congress on Thursday he is considering firing employees in his department's oil royalties office who investigators say were receiving lavish gifts, partying and having sexual relationships with oil company officials.

Kempthorne also told a House panel he would appoint an attorney-adviser to oversee ethics in the Denver office at the center of the scandal. The office is responsible for marketing billions of dollars worth of oil and natural gas energy companies barter to the government in lieu of cash royalty payments for drilling on federal lands, a program known as Royalty-In-Kind.

"I can assure the committee that this process will be completed as swiftly as possible, and we will examine the full spectrum of disciplinary actions, including termination," said Kempthorne, who said he was outraged by employees' abuse of the public's trust. Kempthorne said he was also considering random drug testing for employees. The Royalty-In-Kind program employees were not subject to drug testing, Kempthorne said.

Last week, in three separate reports, Interior Department Inspector General Earl E. Devaney alleged 13 employees in Washington and Denver were rigging bids, accepting expensive gifts and partying with oil company employees from 2002 to 2006. Several employees in the office were using marijuana and cocaine, according to the reports, and a third of the 55 employees in the Denver office accepted gifts from oil and gas companies.

Devaney told members of the House Natural Resources Committee on Thursday the conduct of the Minerals Management Service employees was "egregious" and said he was at a loss to explain the behavior of oil and gas company representatives.

"Simply stated, the MMS employees named in these latest reports had a callous disregard for the rules by which the rest of us are required to play," Devaney said.

Under questioning, Devaney said there was no evidence that any of the personal relationships brought benefits to the oil companies, but he said there should be an outright ban on accepting gifts and gratuities from any industry.

Federal employees are currently barred from accepting individual gifts over $20 and can accept no more than $50 in gifts each year. The nine employees targeted by the investigation accepted thousands of dollars worth of gifts from four oil companies — Shell, Chevron, Hess and Denver-based Gary-Williams Energy. The gifts included meals, ski and golf trips, snowboarding lessons and Toby Keith concert tickets. A Hess official said the company only paid for lunch on several occasions.

"What's the standard of conduct you're developing for the people having conduct with the United States government?" asked Rep. George Miller, D-Calif. "What about the behavior by the private sector here?"

Earlier this week, the House passed legislation that would expand offshore drilling, increasing the royalties collected by the federal government. The bill also would establish penalties and jail time for oil executives and department employees who receive improper gifts.