After an eight-year absence, Delta Air Lines will rejoin the Standard & Poor's 500 stock index after paying down debt and restarting its dividend.

The Atlanta-based airline, the world's second-largest carrier and the dominant airline in Minneapolis-St. Paul, will join the S&P 500 after the close of trading Tuesday, according to S&P Dow Jones Indices. Delta will become the second airline in the benchmark gauge, joining Southwest Airlines. The airline replaces software provider BMC Software Inc., which is being bought by closely held Bain Capital.

Delta, which was removed from the S&P 500 in 2005 before filing for bankruptcy, has seen its market value nearly double to $17.1 billion in 2013. The airline left Chapter 11 protection in 2007, restarted its dividend after a decadelong break and is paying down debt and catching up on pension obligations to improve its credit.

Investment bankers told Delta the company was "on some short list" of possible index additions, President Ed Bastian said in May. S&P's requirements include a market value of more than $4 billion, four consecutive quarters of profits and at least six months of trading after an initial public offering, according to the website.

The revision in the equity index will prompt money managers to shift holdings to match the index. More than $5 trillion is benchmarked to the S&P 500, according to the website.

Delta shares climbed as much as 5.5 percent to $20.99 in after-hours trading Friday. They're up 68 percent for the year, compared with 16 percent for the S&P 500.

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