EX-99

                                                                    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
(collectively, the "Reporting Persons").

(2) The common stock, par value $0.001 per share ("Common Stock") of NYFIX, Inc.
(the "Issuer") was issued in payment of a dividend on the Series B Voting
Convertible Preferred Stock (the "Preferred Stock") 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 such
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 by (ii) the applicable conversion price ($5.00) now
in effect.

(3) Following the dividend discussed in Note 2, WP IX is the direct record owner
of 227,500 shares of Common Stock and 1,500,000 shares of Preferred Stock, which
is convertible into 15,000,000 shares of Common Stock. 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 (the "Act"), 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 all disclaim beneficial ownership of all shares of
Common Stock and Preferred Stock except to the extent of any indirect pecuniary
interest therein.

(4) 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.

(5) The Preferred Stock is convertible, in whole or in part, at any time and
from time to time at the holder's election. At any time after April 12, 2008,
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. The
conversion rights do not expire.

(6) The exercise price of the Warrant to Purchase Common Stock (the "Warrant")
is initially equal to $7.75 per share, subject to certain adjustments in
accordance with the terms of the Warrant.

(7) The Warrant is convertible 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.

(8) WP IX is the direct record owner of the Warrant, which is convertible into
2,250,000 shares of Common Stock. The sole general partner of WP IX is WP LX
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
(the "Act"), 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 LX. Each of WP, WP LLC, WPP LLC, WP IX LLC, Mr. Kaye
and Mr. Landy all disclaim beneficial ownership of the Warrant except to the
extent of any indirect pecuniary interest therein.

EX-99

                                                                    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

                                                                    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:  February 5, 2007
   ------------------------------------------                 ----------------
   Name:   Scott A. Arenare
   Title:  Partner


WARBURG PINCUS PARTNERS, LLC

By:  Warburg Pincus & Co., its Managing Member


By: /s/ Scott A. Arenare                               Date:  February 5, 2007
   ------------------------------------------                 ----------------
   Name:   Scott A. Arenare
   Title:  Partner


WARBURG PINCUS, LLC


By: /s/ Scott A. Arenare                               Date:  February 5, 2007
   ------------------------------------------                 ----------------
   Name:   Scott A. Arenare
   Title:  Managing Director


WARBURG PINCUS & CO.


By: /s/ Scott A. Arenare                               Date:  February 5, 2007
   ------------------------------------------                 ----------------
   Name:   Scott A. Arenare
   Title:  Partner


By: /s/ Scott A. Arenare                               Date:  February 5, 2007
   ------------------------------------------                 ----------------
   Name:   Charles R. Kaye
   By:     Scott A. Arenare, Attorney-in-Fact


By: /s/ Scott A. Arenare                               Date:  February 5, 2007
   ------------------------------------------                 ----------------
   Name:   Joseph P. Landy
   By:     Scott A. Arenare, Attorney-in-Fact