By Jessica Hall

PHILADELPHIA (Reuters) - The energy, finance, technology and healthcare industries are expected to be the hottest areas in a dealmaking market that in 2010 is likely to expand gradually from this year's depressed levels.

This week's move by Exxon Mobil Corp to buy XTO Energy Inc for $30 billion in stock may be a harbinger of activity to come in 2010 as companies flex their stronger share prices and release pent-up deal demand.

The XTO takeover followed other corporate mega-deals, such as the $26 billion cash-and-stock deal for Burlington Northern Santa Fe by Warren Buffett's Berkshire Hathaway, and Comcast Corp's $30 billion planned purchase of NBC Universal.

"We're encouraged by the current activity. The pipeline for the early part of 2010 is improving -- 10 to 15 percent growth for the year is possible. Both engines of activity -- private equity and corporates -- are now active," said Jeffrey Kaplan, global head of mergers, acquisitions, financial sponsors and corporate finance at Bank of America Merrill Lynch.

"You need a sustainable economic recovery," he said. "You cannot expect the M&A market to flourish without favorable economic conditions. The best deals often are done at the beginning of a recovery. Post-bubbles create opportunities to get great values but are not always the best times for sustained M&A activity."

M&A totals $1.968 trillion so far in 2009, down 32 percent from full-year 2008 and down 53 percent from the record high in 2007, according to data from Thomson Reuters.

Graphic: M&A activity in Q4 and 2009 click here