Shares in Motors Liquidation ( MTLQQ) rose Tuesday for the third straight day, perplexing regulators, who say they are reviewing the trading.

The worthless shares closed Tuesday at 52 cents, up 1 cent on volume of 32.8 million shares. They opened Friday, July 17 at 33 cents, after a sharp fall prompted by a name change made so that traders would not mistakenly assume that they are related to General Motors, which emerged from bankruptcy protection July 10. But the shares rose on Friday, Monday and Tuesday. Ford ( F), the only publicly traded American automaker left, closed Tuesday at $6.20, up 1 cent.

The Financial Industry Regulatory Authority is reviewing the trades, says spokeswoman Nancy Condon.

"Bearing in mind that we only have regulatory jurisdiction over securities firms and the individuals associated with them, we would definitely look at the trading associated with these shares, as with any instance where there is unusually high volume or unusual activity in a stock, and especially one with circumstances like these," Condon says.

"We'll be looking at who was buying, who was selling and what the rationale was," she says.

Peter Leeds, publisher of the Toronto-based penny stock newsletter PeterLeeds.com, says: "It's surprising to see how many people are buying a company that is definitely going to zero."

Leeds says he believes some traders are covering short sales, while others believe falsely that if they accumulate enough shares they will be able to influence the course of the bankruptcy negotiations. In reality, equity holders rank behind nearly every other creditor in a bankruptcy, and would have no impact on decisions made in the hearing.

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