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                                                                 EXHIBIT (a)(13)

                         MARATHON OIL COMPANY COMPLETES
                           PENNACO ENERGY TENDER OFFER

HOUSTON, Feb. 6 /PRNewswire/ -- Marathon Oil Company, part of the USX-Marathon
Group (NYSE: MRO), a unit of USX Corporation, announced today that its tender
offer through a subsidiary to acquire all outstanding shares of common stock of
Pennaco Energy, Inc. (AMEX: PN) for $19.00 per share, net to the seller in cash,
without interest, expired at 12:00 midnight, Eastern time, on Monday, February
5, 2001. Marathon has accepted for payment all Pennaco shares validly tendered
and not withdrawn as of the expiration of the offer. Payment for those shares
will be made promptly.

The Bank of New York, the depositary for the offer, has advised Marathon that,
as of the expiration of the offer, approximately 17.6 million shares of Pennaco
common stock (including approximately 1.0 million shares subject to guarantees
of delivery within the next three days) were validly tendered and not withdrawn
in the offer. Those shares represent approximately 87% of the outstanding
Pennaco shares.

Marathon plans to acquire the remaining Pennaco shares through a merger in which
each share of Pennaco common stock not purchased in the offer and not held by
stockholders who have properly exercised dissenters rights under Delaware law
will be converted into the right to receive $19.00 in cash, without interest.
Following the second-step merger, Pennaco will become a wholly owned subsidiary
of Marathon.

Marathon is one of the largest fully integrated oil firms in North America. It
is engaged in the worldwide exploration and production of crude oil and natural
gas and through Marathon Ashland Petroleum LLC, refines, markets and transports
petroleum products in the United States.