HOUSTON, June 12 (Reuters) - A U.S. court overseeing the

auction of shares in Venezuela-owned Citgo Petroleum's parent

has told bidders seeking to acquire the seventh-largest U.S. oil

refiner they may raise their offers after Tuesday's filing

deadline, one of the groups said.

Tuesday was the court's deadline for submitting bids in

the second and final round in a years-long court process to pay

creditors for past expropriations and debt defaults in

Venezuela. At least one credit bid was received by the court.

An ability to raise offers after the deadline increases

the court's chances of approaching a fair value for Citgo in a

sale process that has

attracted big name investors

, including Elliott Investment Management, Centerview

Partners and U.S. energy companies such as ConocoPhillips ( COP )

and Koch Industries.

The highest offer received in a first bidding round in

January was

$7.3 billion

, below Citgo's value of between $11 billion and $13

billion. The 18 creditors registered in Delaware seek to cash

$21.3 billion in claims from the auction.

An attorney for the court official hired to oversee the

auction, Robert Pincus, did not immediately reply to a request

for comment on the bidding process and offers submitted. Boards

supervising Citgo, which severed ties with PDVSA in 2019, did

not reply to requests for comment.

"TOP OFF" BIDS

The bids are being reviewed by Pincus and investment

banking firm Evercore Group. The winner is scheduled to be

confirmed on July 15, under the court's schedule.

Representatives of Venezuela in the case could request a third

round if the second round's offers are too low, sources said

this week.

Bidders have been told they can "top off" their offers,

according to a spokesperson for Gold Reserve ( GDRZF ), one of the

groups that submitted offers this month.

"Whoever submits the winning bid, that bid can be topped

off," to allow a credit offer submitted by a group with a claim

against Venezuela to recoup its full claim, said Jean-Charles

Potvin, a spokesperson for Gold Reserve ( GDRZF ).

The firm used its $1 billion claim against Venezuela to

submit a credit bid. The court also will allow other bidders to

trump the ostensible winner by offering at least $100 million

more, Potvin said.

The $100 million minimum for a higher offer was only

presented to bidders in recent weeks. The amount would prevent

an investor group from submitting slightly higher offer at the

last minute, he said.

Venezuela and some U.S. lawmakers are asking the U.S.

government to

pause the auction

for at least 60 days until a presidential election is

completed in the South American country, which could lead to a

wider debt restructuring process.