The Dow Jones industrial average and the Standard & Poor's 500 index closed at record highs Monday as the market delivered its fourth gain in as many trading days.
Pharmaceutical and technology stocks were among the big risers, while shares in energy companies fell sharply as the decline in oil prices deepened. Discouraging data on U.S. home sales failed to derail the "Santa" rally - what traders often call a pre-Christmas advance.
Trading volume was lighter than usual as many investors looked ahead to the Christmas holiday.
The Standard & Poor's 500 index gained 7.89 points, or 0.38 percent, to 2,078.54. The S&P's most recent record close was 2,075.37, set on Dec. 5.
The Dow Jones industrial average rose 154.64, or 0.87 percent, to 17,959.44. Its last record close was 17,958.79 on Dec. 5.
The Nasdaq composite picked up 16.04 points, or 0.34 percent, to 4,781.42.
The Dow and S&P 500 are both up for the month, while the Nasdaq is down. The three indexes are up for the year.
Pharmaceutical stocks were among those making big moves Monday.
Achillion Pharmaceuticals' shares gained 9 percent after the biotechnology company reported positive results from two studies focusing on a treatment regimen for hepatitis C patients. The stock rose $1.28 to $15.49. Meanwhile, Enanta Pharmaceuticals vaulted 10.1 percent after it received regulatory approval for a hepatitis C treatment. Enanta added $4.70 to $51.32.
Drugmaker Gilead Sciences tumbled 14.3 percent after pharmacy benefits manager Express Scripts said it will no longer cover two of Gilead's hepatitis C drugs as part of an effort to battle the high cost of treatment for the disease. Gilead slid $15.55 to $92.90.
The price of U.S. oil fell. Benchmark U.S. crude fell $1.26 to close at $55.26 a barrel in New York. Oil has plunged since peaking at $107 a barrel in June.
Several oil production and exploration companies tumbled as the slide in oil prices deepened Monday.
Chesapeake Energy slid $1.44, or 7.3 percent, to $18.42. Southwestern Energy dropped $1.69, or 5.5 percent, to $29.31.
In other energy futures trading, wholesale gasoline fell 2.5 cents to close at $1.54 a gallon, while heating oil fell 1.1 cents to close at $1.95 a gallon.
Natural gas fell 32 cents to close at $3.14 per 1,000 cubic feet. Natural gas has fallen 15 percent over the last three trading sessions to its lowest level since January 2013 on forecasts for milder winter weather.