NEW YORK (CNNMoney.com) -- A hedge fund with large stakes in both Delta Air Lines and United Airlines parent UAL Corp. is pushing for those companies to merge to deal with rising jet fuel costs.

Pardus Capital Management, which according to SEC filings has 3 million shares of Delta (Charts, Fortune 500) and 5.6 million shares of UAL (Charts, Fortune 500), sent a letter Tuesday to the airlines proposing a stock-for-stock combination between the two companies that would form the world's largest airline.

United is currently the No. 2 carrier, behind only AMR Corp. (Charts, Fortune 500) unit American Airlines, while Delta, which emerged from bankruptcy earlier this year is No. 3.

Officials from United and Pardus were not immediately available for comment, but Delta issued a statement saying it is open to discussions of some form of combination, and that it was looking for the right deal even before the letter.

"We appreciate receiving Pardus' views on the best course for Delta's future," said the statement from CEO, Richard Anderson. "We have been consistent in our public statements that Delta believes that the right consolidation transaction could generate significant value for our shareholders and employees and that strategic options should be evaluated. With oil at over $90 a barrel, this analysis takes on a heightened importance as we factor those prices into our long-term planning process."

Jet fuel prices have soared about 24 percent since Labor Day and are now 55 percent higher since January, when Delta fought off a hostile takeover attempt launched in 2006 by US Airways Group (Charts, Fortune 500), arguing that such a combination would run afoul of anti-trust regulators and not be a benefit to the airline, its employees or its passengers.

Since Delta fought off the US Air bid, it has gotten a new CEO, Anderson, a veteran of Northwest (Charts) and Continental Airlines (Charts, Fortune 500), who has spoken far more positively about the benefits of industry consolidation. UAL executives have long been on the record in favor of mergers in the industry. To top of page