Shares of Dollar General (DG) are on the rise Tuesday morning after the discount retailer was added to the S&P 500. The stock has even more room to run.

Of course, the shares are up now because fund managers who mimic the S&P 500 are buying it. But Dollar General still has plenty going for it.

The Goodlettsville, Tenn. company is probably taking market share away from rivals such as Wal-Mart (WMT). Same-store sales, a key retail metric of stores opened at least a year, surged an eye-popping 5.1% in the last quarter. That was more than double the 2.2% increase reported at Wal-Mart's U.S. stores, excluding fuel.

U.S. economic growth is expected to be mediocre at best, and most experts predict the unemployment rate will hover around 8% for the foreseeable future. Even if the economy continues to improve, the discount chain's position is pretty secure. Consumers are loath to increase their debt levels significantly, given how badly they were burned during the Great Recession. That isn't going to change any time soon, even as consumer confidence continues to climb and the real estate market rebounds.

Even so, the "good news" does not appear to be fully reflected in Dollar General's stock price, especially given the company's history of exceeding Wall Street expectations. Dollar General trades at a price-to-earnings multiple of 18.87, which is below its five-year high of 22.48 and above Wal-Mart's 14.38 and Target's (TGT) 13.94.

The average 52-week price target on Dollar General is $60.78, up more than 22% from where it currently trades. Shares of the company have gained more than 20% this year. Rival Dollar Tree (DLTR) also has some potential upside. The average 52-week price target on the stock is $48.37, about 14% above where it currently trades. Unlike Dollar General, Dollar Tree is in Wall Street's doghouse after issuing a disappointing earnings outlook. This stock is more risky than Dollar General, which many investors consider to be the better managed of the two.

Like other retailers, Dollar General stands to benefit from the growth in mobile payments. The company recently launched an iPhone and Android apps. Customers who use the programs will be the first to learn about sales and will be able to take advantage of special discounts. Dollar General plans to open 625 new stores and to relocate or remodel 575 locations by the end of the year. It expects to add 7% in square footage.
 
Investors will soon learn if the good times are continuing at Dollar General. The company, which owns 10,000 stores in 40 states, is due to report earnings Dec. 11. Revenue is expected to surge 10.2% to $3.96 billion in the current quarter. Profit is forecast to be 60 cents per share, an increase of 10 cents from a year ago.

Jonathan Berr does not own shares of the listed stocks. Follow him on Twitter@jdberr.