Research has confirmed securities class action leader Milberg Weiss Bershad Hynes & Lerach's dominance of the US plaintiff market – just as the firm finalises its long-awaited split.

The firm, which is breaking up into East Coast and West Coast arms, was involved in 66% of 2003′s class action settlements, accounting for total awards of $2.11bn (£1.17bn) from 65 actions, according to securities litigation monitoring company Securities Class Action Services (SCAS).

The figures illustrate the gulf between Milberg Weiss and the rest of the market, with second-place Bernstein Litowitz Berger & Grossman winning $950.25m (£530m) in awards from nine class actions, and third-place Grant & Eisenhofer settling at a total of $610.5m (£350.5m) from three cases.

SCAS executive director Bruce Carton said: "Securities class actions settlement amounts were at near-historic levels in 2003. These firms led the charge, with one firm, Milberg Weiss, having a hand in more than two-thirds of last year's settlement dollars."

The survey comes as Milberg Weiss prepares to splinter into two, changing the landscape of the plaintiff market in the US.

The arrangement will see most of Milberg Weiss' East Coast practice form 41-partner Milberg Weiss Bershad & Schulman, under the lead of figurehead Melvyn Weiss.

It will have offices in New York, Boca Raton, Delaware and Washington DC as well as outposts in Los Angeles and Seattle.

The West Coast arm of the legacy firm, under the lead of William Lerach, has become a 51-partner practice named Lerach Coughlin Stoia & Robbins.

The San Diego-based outfit will have additional offices in San Francisco, Los Angeles, Philadelphia, Washington DC and Houston.

Weiss said: "This is a very exciting and important time for Milberg Weiss.

"We are experiencing solid growth in key markets and practice areas, and continue to build our own reputation as the leading class action law firm in the country."

Lerach said of his firm: "The new firm has an outstanding team in place. We are well positioned to continue advocating aggressively for investors and consumers alike."

The two sides of the firm put the split down to the difficulty of managing such a large practice, although there are also understood to have been tensions between Weiss and Lerach.