Skadden Arps Slate Meagher & Flom jumped from fourth place at the half-year mark to first place in the US M&A league tables after the first three quarters.
Skadden advised on the third quarter's second-largest deal, the $9.2bn (£5.21bn) United Health-PacifiCare deal, taking it from fourth place by value and volume in the tables to head the volume rankings and moving to second place by value with 124 deals worth $182.7bn (£103.45bn), according to data from Mergermarket.
Simpson Thacher & Bartlett stayed top of the table for M&A by value during the third quarter, taking its annual tally to 82 deals worth $224.7bn (£127.23bn). The New York firm was also the half-year leader in the league tables by volume, but the market was heavily depressed in the third quarter and it slumped to seventh in the table ranked by deal numbers.
Deal activity decreased 27 per cent in the third quarter, with volume down 23 per cent. There was $197.6bn (£111.89bn) of transactions, compared with $270.7bn (£153.28bn) in the second quarter.
Simpson Thacher had a role in the quarter's biggest deal - the $15bn (£8.49bn) Hertz leveraged buyout (LBO) - and advised on the $8bn (£4.53bn) Teva Pharma- ceutical-Ivax Corp deal. The firm's other deals include the $11.3bn (£6.4bn) SunGard Data Systems LBO, Federated Department Stores' $6.6bn (£3.74bn) sale of credit card assets and TPG and Warburg Pincus's $5.1bn (£2.89bn) acquisition of the Neiman Marcus Group.
Weil Gotshal & Manges moved from thirteenth place in the 2004 year-end tables to third by value and volume after its role in the Hertz deal.
Sullivan & Cromwell fell to fourth by value in the third quarter after being second in the previous quarter with 77 deals worth $168.8bn (£95.58bn), including the $21.7bn (£12.29bn) SBC-AT&T deal.