EX-99

Designated Filer: Warburg Pincus Private Equity IX, L.P.
Issuer & Ticker Symbol:   NYFIX, Inc. (NYFX)
Date of Event Requiring Statement:    December 31, 2008

                                                                    Exhibit 99.1

                            Explanation of Responses:


   (1) This Form 4 is filed on behalf of Warburg Pincus Private Equity IX, L.P.,
   a Delaware limited partnership ("WP IX"), Warburg Pincus IX, LLC, a New York
   limited liability company ("WP IX LLC"), Warburg Pincus Partners, LLC, a New
   York limited liability company ("WPP LLC"), Warburg Pincus LLC, a New York
   limited liability company ("WP LLC"), Warburg Pincus & Co., a New York
   general partnership ("WP"), and Messrs. Charles R. Kaye and Joseph P. Landy.

   (2) On December 31, 2008, 525,000 shares of common stock, par value $0.001
   per share ("Common Stock") of NYFIX, Inc. (the "Issuer") were issued to WP IX
   by the Issuer in payment of a dividend on the Series B Voting Convertible
   Preferred Stock (the "Preferred Stock") required to be paid pursuant to the
   Certificate of Designation, a copy of which was attached as Exhibit 3.2 to
   the Issuer's current report on Form 8-K filed with the Securities and
   Exchange Commission on October 18, 2006. The number of shares of Common Stock
   issued in payment of the dividend was determined by dividing (i) the amount
   of the dividend that would have been payable with respect to such share of
   Preferred Stock had such dividend been paid in cash ($1.75) by (ii) the
   applicable conversion price ($5.00) now in effect.

   (3) Following the issuance discussed in note 2, WP IX is the direct record
   owner of 3,850,227 shares of Common Stock, 1,500,000 shares of Preferred
   Stock and a Warrant to purchase an aggregate of 2,250,000 shares of Common
   Stock (the "Warrant"). Each share of Preferred Stock is initially convertible
   into 10 shares of Common Stock at an initial conversion price of $5.00 per
   share, subject to certain adjustments in accordance with the terms of the
   Preferred Stock. The Preferred Stock is convertible, in whole or in part, at
   any time and from time to time at the holder's election. The Preferred Stock
   is convertible at the option of the Issuer, in whole or in part, if the price
   per share of the Common Stock reaches certain levels. Such conversion rights
   do not expire. The exercise price of the Warrant is initially equal to $7.75
   per share, subject to certain adjustments in accordance with the terms of the
   Warrant. The Warrant is exercisable at any time, in whole or in part, at the
   holder's option until 5:00 p.m. Eastern Time on October 12, 2016, at which
   point the Warrant expires.

   (4) The sole general partner of WP IX is WP IX LLC. WPP LLC is the sole
   member of WP IX LLC. WP is the managing member of WPP LLC. WP LLC manages WP
   IX. Charles R. Kaye and Joseph P. Landy are each Managing General Partners of
   WP and Co-Presidents and Managing Members of WP LLC. By reason of the
   provisions of Rule 16a-1 of the Securities Exchange Act of 1934, as amended,
   WP, WP LLC, WPP LLC, WP IX LLC, Mr. Kaye and Mr. Landy may be deemed to be
   the beneficial owners of any securities that may be deemed to be beneficially
   owned by WP IX. Each of WP, WP LLC, WPP LLC, WP IX LLC, Mr. Kaye and Mr.
   Landy disclaims beneficial ownership of all shares of Common Stock and
   Preferred Stock and the Warrant, except to the extent of any indirect
   pecuniary interest therein.

EX-99

Designated Filer: Warburg Pincus Private Equity IX, L.P.
Issuer & Ticker Symbol:   NYFIX, Inc. (NYFX)
Date of Event Requiring Statement:    December 31, 2008

                                                                    Exhibit 99.2

                        JOINT FILERS' NAMES AND ADDRESSES


1.   Name:     Warburg Pincus IX LLC
     Address:  c/o Warburg Pincus LLC
               466 Lexington Avenue
               New York, NY 10017

2.   Name:     Warburg Pincus Partners, LLC
     Address:  c/o Warburg Pincus LLC
               466 Lexington Avenue
               New York, NY 10017

3.   Name:     Warburg Pincus LLC
     Address:  466 Lexington Avenue
               New York, NY 10017

4.   Name:     Warburg Pincus & Co.
     Address:  c/o Warburg Pincus LLC
               466 Lexington Avenue
               New York, NY 10017

5.   Name:     Charles R. Kaye
     Address:  c/o Warburg Pincus LLC
               466 Lexington Avenue
               New York, NY 10017

6.   Name:     Joseph P. Landy
     Address:  c/o Warburg Pincus LLC
               466 Lexington Avenue
               New York, NY 10017

EX-99

Designated Filer: Warburg Pincus Private Equity IX, L.P.
Issuer & Ticker Symbol:   NYFIX, Inc. (NYFX)
Date of Event Requiring Statement:    December 31, 2008

                                                                    Exhibit 99.3

                            JOINT FILERS' SIGNATURES


WARBURG PINCUS IX, LLC

By:  Warburg Pincus Partners, LLC, its Sole Member,
     By:  Warburg Pincus & Co., its Managing Member

By:  /s/ Scott A. Arenare
     ------------------------------                    Date:   January 5, 2009
     Name:   Scott A. Arenare
     Title:  Partner

WARBURG PINCUS PARTNERS, LLC

By:  Warburg Pincus & Co., its Managing Member

By:  /s/ Scott A. Arenare
     ------------------------------                    Date:   January 5, 2009
     Name:   Scott A. Arenare
     Title:  Partner

WARBURG PINCUS LLC

By:  /s/ Scott A. Arenare
     ------------------------------                    Date:   January 5, 2009
     Name:   Scott A. Arenare
     Title:  Managing Director


 WARBURG PINCUS & CO.


By:  /s/ Scott A. Arenare
     ------------------------------                    Date:   January 5, 2009
     Name:  Scott A. Arenare
     Title:  Partner


By:  /s/ Scott A. Arenare
     ------------------------------                    Date:   January 5, 2009
     Name:  Charles R. Kaye
     Title: Scott A. Arenare, Attorney-in-Fact*


By:  /s/ Scott A. Arenare
     ------------------------------                    Date:   January 5, 2009
     Name:  Charles R. Kaye
     Title: Scott A. Arenare, Attorney-in-Fact**

*    Power of Attorney given by Mr. Kaye was previously filed with the SEC on
     March 2, 2006 as an exhibit to a Schedule 13D filed by Building Products,
     LLC with respect to Builders FirstSource, Inc.

**   Power of Attorney given by Mr. Landy was previously filed with the SEC on
     March 2, 2006 as an exhibit to a Schedule 13D filed by Building Products,
     LLC with respect to Builders