The carriers say they will invest $3 billion in upgrades including airport facilities and on-board product such as flat-bed seats in the BusinessElite cabin and extra legroom in Economy Comfort.

Analysts have generally been positive as word of the Delta/Virgin deal leaked out last week. S&P Capital IQ analyst Jim Corridore wrote Tuesday in a note that Delta's investment "will pay off in terms of greater European market share and improved unit revenues.

"We think EU and U.S. regulatory approval is likely, but not certain," Corridore wrote. "This deal, along with DAL's refinery purchase, highlights DAL's stategic vision." He maintained a buy rating.

In a report issued a week ago, JP Morgan analyst Jamie Baker noted that investors sold off Delta shares when word of the detail began to leak out. Baker said, however, that "we would look favorably on an investment up to $350 million." It appears that somebody may have been reading Baker's report.

Delta shares lost 4% on Monday, Dec. 3, the first trading day after media reports of the Virgin deal surfaced. On that day, shares fell from $10 to $9.62. On Monday, Dec. 10, Delta shares closed at $10.14. In premarket trading Tuesday, shares were gaining 14 cents to $10.28.

-- Written by Ted Reed in Charlotte, N.C.

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