Pricing at the top range of bids and tumbling oil prices could make the cash-strapped Venezuelan government less ambiguous towards divesting Citgo. An Oct. 26 El Universal newspaper interview with Venezuelan Finance Minister Rodolfo Marco in which he said Citgo's sale "has been ruled out" stirred confusion among interested parties.

The companies that made bids in December include Marathon Petroleum Corp (>> Marathon Petroleum Corp), Valero Energy Corp (>> Valero Energy Corporation), HollyFrontier Corp (>> HollyFrontier Corp) and a consortium of TPG Capital LP and Riverstone Holdings LLC, the people familiar with the matter said. They asked not to be identified because the matter is confidential.

They said some bids came in at more than $10 billion while others were below $7 billion. Bidders have taken different views on the fluctuating value of crude oil held at the refineries, future crude oil purchases from OPEC member Venezuela and potential environmental liabilities, the people said.

Citgo declined to comment.

Citgo runs three refineries in the United States with a total capacity of 750,000 barrels per day. The party that acquires all of them would have major refining capacity in the U.S. Midwest and on the Gulf Coast, benefiting from a boom in U.S. oil production.

Lazard Ltd (>> Lazard Ltd), the investment bank hired by Venezuela's state-run PDVSA to explore a sale of Citgo, has not told bidders if there will be an additional round of bids, the people familiar with the matter said.

Representatives for Lazard, PDVSA, Marathon Petroleum and HollyFrontier did not return requests for comment. Representatives for TPG, Valero and Riverstone declined to comment.

A first round of bids this fall attracted other contenders including India's Reliance Industries Ltd (>> Reliance Industries Limited) and PBF Energy Inc (>> PBF Energy Inc). Those parties are no longer in the running, the people said.

Venezuela faces a string of international arbitration cases as a result of nationalizations under the late President Hugo Chavez's socialist government. A sale of the U.S. refineries would eliminate the possibility of them being seized should a court rule against Venezuela.

ConocoPhillips (>> ConocoPhillips) said last month in a Texas court filing that the Venezuelan government is using the sale of Citgo to hinder ConocoPhillips' ability to collect an expected arbitration award after its oil assets were nationalized in Venezuela in 2007.

Citgo pays out hefty dividends to its owner, state-owned oil company PDVSA. Lower oil prices are adding to Venezuela's debt woes because they weigh on the revenue it generates from oil production, making it more open to raising cash via a sale of Citgo.

Citgo's U.S. refineries are in Lemont, Illinois; Lake Charles, Louisiana; and Corpus Christi, Texas. Citgo also has 48 oil terminals. PDVSA also has a 50 percent stake in the Chalmette refinery in Louisiana alongside Exxon Mobil Corp (>> Exxon Mobil Corporation), which owns the rest.

(Reporting by Mike Stone and Jessica Resnick-Ault in New York and Marianna Parraga in Houston, Texas; Editing by Grant McCool)

By Mike Stone and Jessica Resnick-Ault