The rush to merge has been driven by low borrowing costs and steady but unspectacular growth in the U.S. economy, which have sent CEOs hunting for new ways to expand sales and boost earnings. "The mega-mergers, the big deals, have come back into favor," says Neil Dhar, U.S. capital markets leader at professional services firm PwC. The combination will boost Shell's oil and gas reserves by 25 percent and give it a bigger presence in the fast-growing liquefied natural gas market. In the U.S., the biggest deal announced is Charter Communications' bid for Time Warner Cable, part of a broader consolidation among cable and media companies as technology and costs shake up the industries. Even if the Fed increases rates later this year, as many economists expect, the enthusiasm for deals will remain, says Bill Wolfe, a senior vice president at Moody's Investors Service. Soon after the merger, AOL's subscription revenues plunged as broadband connections replaced its dial-up services.