According to Bloomberg, the Asia-Pacific region bucked the trend of a global 12 per cent drop in M&A activity for Q3 2011, when compared with the same period last year. The Asia-Pacific region had a 4 per cent increase in activity as compared to 12 months ago, in stark contrast to Europe, the Middle East and Africa, which experienced a 30 per cent reduction in M&A activity.

Despite the recent arrival of large global law firms in Australia, national firms came out on top for both deal count and deal value.

According to Bloomberg, Minter Ellison has acted on the most announced deals for the first nine months of this year (57), with Allens Arthur Robinson having the largest share of deal value, with $US42.6 billion ($44.2 billion).

Allens is also ranked second for deal count, behind Minters, with Mallesons Stephen Jaques, Freehills and Clayton Utz rounding out the top five.

"We haven't seen the global law firms impact our client base or work flow too much so far," said Allens Brisbane-based M&A partner Chelsea Drake. "We had a very successful year last year despite the arrival of A&O and Clifford Chance ... and we have also been very successful so far this year."

Both Allens and A&O acted on the $9.9 billion SABMiller takeover of Foster's, with Allens also advising on notable deals such as the $4 billion merger between the Seven Media Group and West Australian Newspapers.

By announced deal value, Mallesons ($US35.9 billion), Simpson Thatcher & Bartlett LLP ($US33 billion), Freehills ($US30.4 billion) and Clayton Utz ($US27.7 billion) round out the top five after Allens.

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English-based global law firms Clifford Chance and Allen & Overy, which have offices in Sydney and Perth, ranked tenthand fourteenth respectively by deal count. A&O also ranked sixth by deal value.

Some notable movers in the rankings included Corrs Chambers Westgarth, which moved from last year's ranking of tenth to sixth by deal volume, and Jones Day, the American-based global firm with an office in Sydney, moved from a ranking of fifteenth to eleventh.

Thomson Reuters also released its worldwide M&A legal advisory league tables for announced deals for the year to the end of September.

According to Thomson, while worldwide M&A activity is up by 22 per cent on the first nine months of 2010, quarterly volume fell by 18 per cent between July and September.

Simpson Thatcher & Bartlett, Sullivan & Cromwell, Davis Polk & Wardell, Latham & Watkins and Freshfields Bruckhaus Deringer are the leading global law firms by deal value for the first nine months of 2011, according to Thomson Reuters.

Clayton Utz and Mallesons are the leading Australian firms, ranked eighteenth and twenty fourth respectively.

The Thomson survey showed a slight increase in Q3 M&A activity in Asia, as compared to Q3 2010, but noted a global quarterly fall of 18 per cent.

"There has certainly been growing uncertainly in global markets over the last few weeks, but it has not impacted on deal flows in the Australian market yet," said Drake. "There seems to be an insatiable appetite for resources in Australia, so the Australian M&A market should continue to be insulated due to the amount of resources work."