ECNs or "Electronic Communication Networks" are computerized trading networks that match buy and sell orders directly, without the help of a traditional marketmaker. 4-letter Nasdaq Level 2 market maker identifiers displayed in brackets.

• Archipelago ECN (ARCA) The Archipelago ECN was formed in December 1996 and is one of the four original ECNs approved in January 1997 by the Securities and Exchange Commission.

• ATTAIN ECN (ATTN)

• BLOOMBERG TRADEBOOK ECN (BTRD) gives institutional investors direct electronic access to many of the world's leading exchanges

• Brut ECN (BRUT)

• Instinet ECN (INCA) Instinet, through affiliates, is the largest global electronic agency securities broker and has been providing investors with electronic trading solutions for more than 30 years.

• Island ECN (ISLD)

• Market XT (MKXT)

• Redibook ECN (REDI)