Credit Suisse, JP Morgan, Deutsche Bank, Bank of America, Bear Stearns and Knight Capital have come over to Bids in a series of undisclosed deals.
They will now join founder members of the system Goldman Sachs, Merrill Lynch, Lehman Brothers, Citigroup, Morgan Stanley and UBS when the system is launched in spring 2007.
Commenting on the deals, Bids CEO Tim Mahoney said: "This level of industry support prior to our launch validates our model and helps build tremendous momentum in advance of the launch of the system.
"We are confident that our model will empower traders by giving them the tools they need to successfully execute block trades," he added.
The platform's chief use will be for block trades, for which it allows improved levels of anonymity and offers access to both buyers and sellers in the deal.
News of the banks signing up to Bids comes at a time of new regulations from the New York Stock Exchange designed to limit the damage that can be done by large stock trades when the market is already in decline.