Skadden Arps Slate Meagher & Flom and Wachtell Lipton Rosen & Katz follow closely with deals worth $302.12bn (£159.45bn) and $251.04bn (£132.49bn) respectively. Simpson Thacher came fourth with $230.45bn (£121.62bn).
In March Sullivan & Cromwell scooped a lead role on the $67bn (£35.36bn) merger between US telecoms companies AT&T and BellSouth. The firm pipped Wachtell to the deal after Sullivan client SBC Communications acquired AT&T, a longstanding Wachtell client. Fried Frank Harris Shriver & Jacobson advised BellSouth and rose seven places to sixth, with $140.91bn (£74.37bn).
Kilpatrick Stockton is the highest climber in Merger- market's half-year M&A deal table, rising 238 places to twelfth, with $90bn (£47.5bn) worth of deals.
Skadden tops the US midmarket table, advising on 41 deals worth less than $250m (£131.94m), to reach a total value of $4.43bn (£2.34bn).
DLA Piper Rudnick Gray Cary and Clifford Chance reached the top 10 on deals volume, picking up instructions on 78 and 53 deals respectively.