Merger and acquisition activity in the Asia-Pacific continued to slow during the first six months of this year, as deal volume dropped to its lowest level in three years.

According to reports published by Bloomberg LP, Thomson Reuters and Mergermarket, deal volume in Asia fell sharply compared to the previous two years.

Rankings by the three organizations, which use different methodologies, did not produce a consensus on a single law firm that advised the most M&A deals by value in the past six months. Simpson Thacher & Bartlett topped Bloomberg's list with $24.3 billion in M&A deal volume in the Asia Pacific, excluding Japan. The New York firm was followed by China's Fangda Partners, Clifford Chance and Korea's Kim & Chang, all totaling more than $20 billion worth of deals in the first half of 2017.

Herbert Smith Freehills won the top spot on Thomson Reuters' ranking with $22.7 billion, and Clifford Chance followed with $21.5 billion. King & Wood Mallesons kept its top ranking from a year earlier on Mergermarket's report with $29.5 billion worth of deals; Clifford Chance and Fangda followed, with each handling deals valued at close to $22 billion.

In 2016, Bloomberg ranked Simpson Thacher as the top M&A legal advisor in the Asia Pacific, excluding Japan, for the first six months, with $71.6 billion. Davis Polk & Wardwell and White & Case led the rankings for Thomson Reuters and Mergermarket in the same period, with $65.8 billion and $66.5 billion, respectively. A significant portion of these firms' deal volume came from a single deal: China National Chemical Corp.'s $46.3 billion acquisition of Swiss agribusiness company Syngenta A.G.

The big-ticket deals of the first half of 2017 dropped even further when compared to the same period of 2015, when no single deal tilted the the balance. That year, top M&A advisors Skadden, Arps, Slate, Meagher & Flom ( by Bloomberg ) and Freshfields Bruckhaus Deringer (By Thomson Reuters and Mergermarket) handled deals worth $95 billion and more than $120 billion, respectively.

Despite using different methodologies, all three organizations found M&A volume across the Asia Pacific during the first half of 2017 to be the lowest since the same period of 2014. Year on year, the total value of M&A deals in the Asia Pacific recorded by Bloomberg dropped 34 percent to $406.8 billion from $612.2 billion; Thomson Reuters recorded a 19 percent year-on-year decrease in total M&A volume, while Mergermarket reported a 15 percent fall.

All three reports indicated a retreat from the strong outbound trend last year. According to Bloomberg's data, 91.7 percent of the M&A activity in the Asia Pacific during the first six months of this year were inbound deals. Mergermarket reported an overall 58 percent decrease in outbound deal volume across the Asia Pacific, totaling only $55.7 billion from 268 deals.

Outbound deals emanating from China declined by a dramatic 49 percent compared to the same period last year a drop attributed to the Chinese government tightening control of capital outflow. But the decline wasn't all due to China. M&A deals in Southeast Asia also slowed. Bloomberg recorded $53.5 billion in deal volume among the 10 countries known as the Association of Southeast Asian Nations, or ASEAN, during the first half of this year the lowest half-year volume since the same period in 2012.

Even the big deals are getting smaller. According to Thomson Reuters, which records the 10 largest M&A deals in the Asia Pacific excluding Japan, five deals were worth $5 billion or above in 2017; in 2016, nine were worth more than that amount, and in 2015, all 10 deals were above $5 billion.

Still, the largest M&A deal out of the Asia Pacific during the first half of 2017 was China Investment Corp.'s $13.8 billion acquisition of Blackstone's European warehouse portfolio company Logicor, announced in June. Clifford Chance is acting for China Investment, while Simpson Thacher & Bartlett is representing longtime client Blackstone.

Things hardly look better in Japan. The country's M&A activity totaled $62.8 billion during the first half of 2017, down 13 percent from a year earlier. This marks a second consecutive year of decline, according to Thomson Reuters' data. It's also the slowest first-half volume since 2013. Morrison & Foerster topped all three rankings for Japan-related deals.