Bank of America, Credit Suisse and UBS have joined Opus-5, a bank-backed electronic trading platform for unregistered securities.
Citi, Lehman Brothers, Merrill Lynch, Morgan Stanley and The Bank of New York Mellon said in August that they were setting up the Open Platform for Unregistered Securities (Opus-5).
The system is being established to provide an alternative to so-called private stock trading platforms operated by Goldman Sachs and JPMorgan Chase.
The Opus-5 platform will provide trade reservation, shareholder tracking and transfer management for privately offered equity trades - known as 144A securities after the SEC rule that deals with private placements of stock.
Last month US stock market operator Nasdaq launched its own electronic 144A securities market. The Web-based application is an extension of Nasdaq's Portal application and enables qualified institutional investors to trade stocks in companies that are not yet public.
Investment bank Bear Stearns has also launched an electronic trading platform for unregistered securities in the US, called Best Markets.