Shares of Dollar General ( DG - Get Report) were among the NYSE's winners Monday, soaring 27% after the retailer agreed to be acquired by Kohlberg Kravis Roberts for about $6.9 billion.

The private equity firm will pay $22 a share, representing a 31% premium to Dollar General's closing price of $16.78 on Friday. Including the assumption of debt, the deal is worth about $7.3 billion. The transaction is expected to close during the third quarter.

Shares of Dollar General were trading up $4.48 to $21.26. The deal sent shares of competitor Family Dollar Stores ( FDO) up 10% to $31.43, while Dollar Tree ( DLTR - Get Report) was adding 80 cents, or 2.2%, to $36.46.

Sierra Health Systems surged 16% after the health care services company agreed to be acquired by UnitedHealth Group ( UNH) for about $2.6 billion in cash. The deal is worth $43.50 a share, representing a 21% premium over Sierra Health's closing price of $35.90 on Friday. The acquisition is expected to close by the end of 2007 or sooner. Shares of Sierra Health were up $5.63 to $41.53.

Shares of Spartech ( SEH) rose 8% after the plastics maker posted better-than-expected first-quarter earnings. For the period ended Feb. 3, the company earned $8.1 million, or 25 cents a share, on revenue of $347.3 million. Analysts polled by Thomson First Call expected earnings of 20 cents a share and a top line of $349.8 million. A year earlier, the company earned $5.7 million, or 18 cents a share, on revenue of $343.6 million.

For 2007, Spartech now sees earnings of $1.55 to $1.62 a share. Previously, the company predicted earnings of $1.55 to $1.60 a share. Analysts project earnings of $1.57 a share. Shares were adding $2.07 to $28.38.

Shares of Steel Dynamics ( STLD - Get Report) rose modestly after the steel company boosted its first-quarter earnings forecast. The company now sees earnings of 94 cents to 98 cents a share, up from an earlier view of 85 cents to 90 cents a share. Analysts project earnings of 88 cents a share. The company said market conditions for flat-rolled steels have improved since mid-January. Shares were trading up 25 cents to $39.03.

Suntech Power Holdings ( STP) fell 5% after the maker of solar-power cells posted mixed fourth-quarter results. The company reported adjusted earnings of $35.5 million, or 23 cents a share, on revenue of $217.9 million. The bottom line topped analysts' expectation of 20 cents a share, but the revenue was shy of Wall Street's projection of $221.4 million. In the year-earlier quarter, Suntech recorded adjusted earnings of $16.8 million, or 13 cents a share, on revenue of $89 million.

Looking ahead, Suntech forecast first-quarter revenue of $220 million to $228 million. Analysts project revenue of $232.9 million. Shares were down $1.99 to $37.31.

Shares of Energy Partners ( EPL) traded actively after the oil and gas concern said that a review of strategic alternatives resulted in no definitive offers for the company to be acquired. Instead of a sale, the company plans to buy back up to 8.7 million of its shares, or 22% of its outstanding stock, in a tender offer of $23 a share. Energy Partners may repurchase another $50 million of stock following the conclusion of the current offer, which is valued at $200 million. Shares were trading down 8 cents to $17.92 on more than triple their average daily volume.

NYSE volume leaders included Motorola , up 19 cents to $18.66; CVS ( CVS), down 51 cents to $32.09; Ford ( F), down 5 cents to $7.88; Caremark , down $1.16 to $60.74; General Electric ( GE), down 13 cents to $34.19; Altria ( MO), up 14 cents to $87; Taiwan Semiconductor ( TSM), up 24 cents to $10.99; and EMC ( EMC), down 5 cents to $13.

Among Nasdaq's volume leaders were Sun Microsystems ( SUNW), up 6 cents to $6.33; Intel ( INTC), up 9 cents to $19.19; Level 3 Communications ( LVLT), down 1 cent to $6.31; Sirius Satellite Radio ( SIRI), down 2 cents to $3.40; Amgen ( AMGN), down $1.57 to $59.29; and Microsoft ( MSFT), down 4 cents to $27.25.