HOUSTON (Reuters) - The second bidding round for shares in refiner Citgo Petroleum's parent was "successful," with several competitive bids received last month by a U.S. federal court, a representative of the court officer overseeing the sale process said on Tuesday.

The case, aimed at paying up to $21.3 billion to creditors for past expropriations and debt defaults in Venezuela, was introduced by miner Crystallex in 2017 and has since allowed a dozen and a half companies to pursue proceeds from the court-organized auction.

Parties representing Venezuela called the first bidding round in January "disappointing" as the highest offer was $7.3 billion, away from a valuation of between $11 billion and $13 billion of the seventh largest U.S. refiner, owned by Venezuela.

The second round bidders and the amount of their offers were not disclosed in a court hearing on Tuesday. A lawyer representing Citgo and its parent PDV Holding, said the companies have not had access to the identity of the bidders.

Citgo and boards supervising the refiner did not reply to requests for comment.

Last month, Canada-incorporated miner Gold Reserve ( GDRZF ) said it submitted a credit bid. Trading house Vitol and refiner CVR Energy ( CVI ) also are among companies that participated in the second round, Reuters reported.

In recent weeks, financial allies began to build to support some of the bids, including firms JP Morgan, Morgan Stanley ( MS ), Rotschild & Co and Wells Fargo ( WFC ), sources have said.

Vitol, CVR Energy ( CVI ), JP Morgan, Morgan Stanley ( MS ), Rotschild & Co and Wells Fargo ( WFC ) declined comment.

The offers have proven to be complex, with many combining cash with credits bids.

Delaware judge Leonard Stark approved a motion to postpone the case's final hearing to September 19, giving more time to evaluate the bids and select a winner, which should be informed around July 31.

The U.S. Justice Department issued a letter this week supporting an extension of the sales process to avoid interference with Venezuela's presidential election on July 28, one of the lawyers representing the Venezuelan parties said in the hearing.