NEW YORK (TheStreet) -- The S&P 500 was trading flat on Monday as energy stocks were slammed on bearish sentiment surrounding crude oil. 

Stocks were on a tear last week after Federal Reserve Chair Janet Yellen and colleagues said the central bank would remain "patient" in its approach to interest rate hikes.

The Dow Jones Industrial Average climbed 0.37%, and the Nasdaq fell 0.05%. 

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Oil prices fell Monday with West Texas Intermediate crude down 2.1% to $55.91 a barrel after a brief rebound earlier. Saudi Arabian Oil Minister Ali al-Naimi said his country was prepared to increase output to meet the demands of new customers, according to Saudi newspaper al-Hayat

Major oil companies were in the red Monday with Exxon Mobil (XOM) - Get Report , Chevron (CVX) - Get Report , Schlumberger (SLB) - Get Report and Halliburton (HAL) - Get Report  lower. The Energy Select Sector SPDR ETF (XLE) - Get Report slid 1.8%.

As Wall Street enters its final two holiday-shortened weeks of the year, trading volume likely will remain light and corporate announcements scant. Existing home sales slid 6.1% to 4.93 million in November, down from 5.25 million a month earlier and missing estimates of an annualized pace of 5.17 million.  

Economic growth significantly improved in November, according to the Chicago Fed national activity index Monday. The index increased to 0.73 from an upwardly revised 0.31 in October, while the three-month average jumped its highest point since May 2010.

BlackBerry (BBRY) added 3.9% as TD Securities issued an upgrade to "buy." Analysts said the smartphone maker is "effectively transitioning to a cross-platform software/services company" and that weak device sales are not indicative of the company's future. 

Express Scripts (ESRX) and AbbVie (ABBV) - Get Report were mixed after reaching an exclusive hepatitis C pharmacy deal. AbbVie shares slipped 0.75% and Express jumped 1.2%.

Sony (SNE) - Get Report shares were gaining nearly 1% after the company's attorney said the company was "still exploring options" as to the distribution of The Interview, the controversial movie that triggered hacker attacks against the studio.

American Apparel (APP) shares were gaining 7.5% after the company adopted a new stockholder rights plan. The stock has been rallying since the retailer officially terminated divisive CEO Dov Charney last week.

Boeing (BA) - Get Report shares were up more than 1% after announcing that Air China has committed to purchase 60 737s, including Next-Generation 737 and 737 MAX airplanes, valued at more than $6 billion at current list prices.

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-- Written by Keris Alison Lahiff in New York.