With 2013 past its halfway point, Davis Polk & Wardwell sits atop three separate rankings of M&A legal advisers based on deal volume during the year's first six months.

The firm topped the so-called league tables released within the last week by Bloomberg, Mergermarket, and Thomson Reuters, all of which rank law firms based on the total value of their corporate clients' M&A transactions during the first half of 2013.

Davis Polk outpaced its rivals on the three lists by advising on at least 50 announced transactions—including a handful of the largest deals so far this year—worth more than $115 billion combined, according to the three separate reports.

As The Am Law Daily has reported in the past, the three outlets rely on different metrics when ranking legal advisers, making the lists most useful as tools that offer a broad look at which law firms are most actively involved in the M&A market.

Bloomberg and Thomson Reuters both identified Jones Day as the first half's top firm based on total transactions with, respectively, 173 and 163 deals. DLA Piper topped Mergermarket's comparable ranking with 152 deals during that period.

Latham & Watkins finished in the second spot behind Davis Polk on both the Mergermarket and Thomson Reuters lists assessing total deal value in the first half of 2013. Latham placed third in Bloomberg's ranking, with Wachtell Lipton Rosen & Katz grabbing the second spot. Skadden, Arps, Slate, Meagher & Flom placed third in both the Mergermarket and Thomson Reuters rankings.

Davis Polk enjoyed a significant surge in the first round of this year's rankings—which covered 2013's first quarter and were released in April—and claimed the top spot on the Thomson Reuters list after placing 18th on that outlet's rankings at the same point last year. The boost was largely the product of the firm's work on two deals that remain among the year's largest: the $28 billion sale of H.J. Heinz Company to Berkshire Hathaway and 3G Capital, and Comcast's $16.7 billion purchase of General Electric's remaining 49 percent stake in NBCUniversal.

Davis Polk padded its lead during the second quarter by landing a role representing Pfizer Inc.'s financial brokers on the company's sale of its remaining stock in animal health company Zoetis Inc. in a deal that Thomson Reuters valued at more than $13 billion. (Skadden advised Pfizer on the transaction.)

Aside from a handful of exceptions, the year has seen a sharp decline in the type of high-priced transactions that generate work for Am Law firms. In a report issued last week, accounting firm Ernst & Young found that global M&A deal value has entered a "triple dip recession," with month-to-month deal values falling short of totals from the same month in the previous year three times since the market's prerecession peak. Worldwide M&A value in the first half of 2013 was down 12 percent from the same period last year—despite a strong showing in the U.S. market, where overall deal value increased 43 percent over the previous year's first half—according to Ernst & Young.

The three outlets issuing league tables identified similar struggles in the global M&A market. Bloomberg reports that global deal volume in the second quarter was up by 3 percent over last quarter, but down 10 percent from the same period last year. Mergermarket, meanwhile, said the total value of global M&A deals in the first half of 2013, $899.1 billion, was the lowest since the $888.4 billion in deals announced during the first half of 2010.