U.S. stocks extended losses in the final hour of trading Monday after crude oil closed at its lowest level since February 2009. 

The S&P 500 fell 1.1%, the Dow Jones Industrial Average declined 1.1%, and the Nasdaq slid 1.1%.

Crude oil prices tumbled after a meeting of the Organization of Petroleum Exporting Countries last week failed to produce output cuts. Global oil prices have been under pressure as demand slows while production remains near record highs. West Texas Intermediate crude fell 5.8% to $37.65 a barrel on Monday.

"Oil prices are on the decline in the aftermath of Friday's OPEC meeting which failed to result in agreement on output targets," Lindsey Piegza, chief economist at Stifel, wrote in a note. "Already, energy analysts are discussing the possibility of $20 a barrel which could pose serious headwinds to next year's growth outlook."

Energy stocks were sharply lower. Major oilers including Exxon Mobil (XOM - Get Report) , Chevron (CVX - Get Report) , PetroChina (PTR - Get Report) , Royal Dutch Shell (RDS.A - Get Report) and BP (BP - Get Report) were more than 2% lower, while the Energy Select Sector SPDR ETF (XLE - Get Report) slumped 4.6%.

Chipotle (CMG - Get Report) slumped 2.9% after the burrito chain warned that comparable sales would fall 8% to 11% in the fourth quarter as a result of an E. coli outbreak. Cases have recently been reported in three more states -- Illinois, Maryland and Pennsylvania. The outbreak has spread to nine states and affected 52 people.

Keurig Green Mountain (GMCR) shares surged more than 72% after the company agreed to be bought by JAB Holding in a deal worth $13.9 billion. Keurig shareholders will receive $92 in cash for each share they hold. The stock closed Friday at $51.70.

General Electric ( GE - Get Report) fell slightly after the company scrapped plans to sell its appliance business to Electrolux ( ELUXY) . The two companies were being sued by the Justice Department to stop the deal which would combine the second- and third-largest appliance manufacturers in the U.S.

Bluebird Bio (BLUE - Get Report) fell more than 35% after reporting mixed results from its gene therapy study into severe sickle cell patients. Two sickle cell patients infused with Bluebird's gene therapy have only shown small improvement after many months.

Activist investor Carl Icahn's Icahn Enterprises has offered to buy Pep Boys  (PBY) for $15.50 a share in cash just days after Icahn disclosed a 12.12% stake in the company. The auto chain has already reached a deal to be acquired by Bridgestone for $15 a share. 

Marvell Technology (MRVL - Get Report) fell more than 1% after reporting a preliminary third-quarter loss of 12 cents a share, well below 22 cents a share in profit a year earlier. The tech company said revenue fell 5%, dragged on by a 16% decline in storage sales. Marvell also said the Securities and Exchange Commission had been in contact regarding an accounting audit.

Gun stocks pushed higher on Monday after a speech from President Barack Obama on Sunday evening called for tighter regulation of firearms. Smith & Wesson (SWHC) and Sturm Ruger (RGR - Get Report) jumped around 6% each. 

Office Depot (ODP - Get Report) shares tumbled more than 10% after the U.S. Federal Trade Commission filed a complaint against Staples  (SPLS) for its proposed takeover. Regulators said the $6.3 billion acquisition would create the largest U.S. retailer of office supplies with little competition.