By Kristina Peterson NEW YORK (MarketWatch) -- U.S. stocks rallied Monday, as bulls made an early bid to extend the markets' three-week winning streak to four, after the group in charge of dating the starts and ends of economic downturns declared that the U.S. recession ended last summer. "It doesn't mean growth is robust, but it is growth," Paul Nolte, managing director at Dearborn Partners, said of Monday's declaration by the National Bureau of Economic Research that the longest U.S. recession since World War II ended in June 2009. Not far from session highs, the Dow Jones Industrial Average (DJI) was recently up 137.44 points, or 1.3%, to 10,745.07. All but one of the Dow's 30 components rose, including International Business Machines Corp. (IBM), which was up 1.4% after the company said it would buy business-software firm Netezza Corp. (NZ) for $1.7 billion. "Companies are flush with cash, and valuations are pretty cheap, so I would think M&A is only going to accelerate for the next six months," said Maris Ogg, president at Tower Bridge Advisors. The S&P 500 (SPX) gained 15.35 points, or 1.4%, to 1,140.94, with energy leading late-afternoon gains among its 10 industry groups. The Nasdaq Composite Index (RIXF) advanced 31.98 points, or 1.4%, to 2,347.59. Four stocks advanced for every one on the decline on the New York Stock Exchange, where 530 million shares had been exchanged as of 2:45 p.m. Eastern time. The NBER report propelled the S&P 500 past levels not breached since May, with investor sentiment already having been bolstered when home builder Lennar Corp. (LEN) topped forecasts, reporting a better-than-expected quarterly profit and a drop in orders that proved less dreary than those experienced by others in its industry. "Buyers were able to take the S&P above 1,131 resistance. If the S&P closes above 1,131, rally hats will be on," Elliot Spar, market strategist at Stifel, Nicolaus & Co., wrote in a note. The National Association of Home Builders reported that its monthly index of builder sentiment remained unchanged in September at an 18-month low. Read more about home builders' sentiment. In its report, the NBER cautioned that its finding did not represent a forecast about the future, saying that if another downturn occurs it would represent a separate recession -- a scenario viewed as unlikely by most economists -- rather than the much-discussed "double dip." Investor sentiment has turned "more positive because the economic news has been better than feared, so it's more a sigh of relief," Ogg said of Wall Street's recent climb.