HOUSTON (Reuters) - A U.S. federal court will likely extend a period for reviewing bids submitted in an auction of shares in the parent of Venezuela-owned refiner Citgo Petroleum, three people close to the matter said, which would delay a resolution to the seven-year-long case.

The court-organized auction of the seventh-largest U.S. oil refiner aims to satisfy up to $21.3 billion in claims against Venezuela for expropriations and debt defaults. The process could lead to new owners of Venezuela's foreign crown jewel.

The court had planned to finish the sale, after two bidding rounds, on July 15, days before Venezuela's presidential election on July 28, which Washington sees as a possible exit to the South American country's long-standing political crisis.

But offers submitted in the second round have proven to be more complex than expected, with several combining cash with credit bids from some of the 18 creditors cleared by the court, the sources said.

Bidders also were asked to disclose whether their bids included plans to pay holders of a bond collateralized with equity in a Citgo parent, adding another level of complexity.

"The investment bankers are trying to equalize - make apples to apples comparisons. That might take a little longer than was hoped," one of the people said.

Citgo operates three refineries that can process up to 807,000 barrels per day of crude oil into fuels and owns a network of storage terminals and pipelines. In 2019, it severed ties with its ultimate parent, Caracas-headquartered state oil company PDVSA.

President Nicolas Maduro's administration and his political opposition have requested the U.S. government to delay or halt the auction, so its results do not alter the election outcome.

In a first bidding round in January, the highest offer submitted was $7.3 billion, less than the market valuation of $11 billion to $13 billion for the refiner.

Lawyers representing Venezuela called the bids "disappointing" and recently have pressed the court to organize a third round if offers in the second round that finished this month do not approach a fair value for the company.

At least five groups of investors submitted binding bids in the second round, and three secured financing commitments from banks and advisors including JPMorgan ( JPM ), Morgan Stanley ( MS ) and Rothschild & Co, people close to the matter told Reuters this month.

The court has yet to disclose the number of bids in the second round or their amounts.

Citgo, boards supervising the refiner and a court officer appointed to oversee the auction did not immediately respond to requests for comment.

"There are 100 reasons why this auction should not be in a hurry," said a person familiar with the sale process, noting the proximity of Venezuela's presidential election.

"There is the possibility of a new government coming along that will honor its obligations ... and it doesn't want this asset to be sold. The court could exhibit a little judiciousness, a little restraint, and see what happens," the person added.