Stocks down as oil prices slide

Stock indexes fell Monday afternoon, the first day since the market's biggest weekly loss in 2½ years, as the price of oil continued a six-month slide. The Russian ruble has plunged to a record low against the dollar.

At midafternoon on Wall Street, the Standard & Poor's 500 index was down 8 points, or 0.4 percent, to 1,994.7. The Dow Jones industrial average gave up 61.5 points, or 0.4 percent, to 17,219. The Nasdaq composite lost 35.7 points, or 0.8 percent, to 4,617.8.

The S&P 500 dropped 3.5 percent last week, its biggest decline since May 2012.

OIL: The price of oil dropped, erasing an early gain. Benchmark U.S. crude fell $1.90, or 3.3 percent, to close at $55.91 a barrel on the New York Mercantile Exchange. Oil has fallen by about half since June on waning global demand and abundant supplies. The recent drop to five-year lows has been roiling stock markets.

RUSSIA'S PAIN: The ruble sank 13 percent to 65.83 to the dollar. The ruble started the year at 32.85 to the dollar. The falling price of oil, which is the chief source of Russian exports and tax revenue, has weighed heavily on the currency.

BUYOUT BOUNCE: Riverbed Technology and PetSmart are soaring on news that they agreed to be bought. Riverbed, a maker of computer-network equipment, jumped $1.61, or 9 percent, to $20.35 after agreeing to a $3.6 billion sale to private-equity firm Thoma Bravo and a Canadian pension fund. Pet-supplies chain PetSmart rose $3.26, or 4.3 percent, to $80.92 after announcing Sunday that it had agreed to an $8.7 billion sale to a group of investors led by BC Partners.

FACTORY FIX: U.S. manufacturing output in November surpassed its pre-recession peak as auto production ramped up. The Federal Reserve figures are an encouraging sign that America's factories are somewhat insulated from the global economic slowdown.

NEXT UP: A two-day meeting of the Federal Reserve begins Tuesday after which the central bank will release a statement that could move markets. Investors will be looking to see if the statement keeps two key words: "considerable time," a reference to how long the Fed plans to keep short-term interest rates near zero. Those low rates are widely credited with helping stocks race higher over the past in the nearly six-year bull market.

Most economists think the Fed will wait until June to raise rates.