Designated Filer: William H. Janeway
Issuer & Ticker Symbol:   NYFIX, Inc. (NYFX)
Date of Event Requiring Statement:    December 31, 2008

                                                                    Exhibit 99.1


                            Explanation of Responses:


   (1) 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
   Warburg Pincus Private Equity IX, L.P., a Delaware limited partnership ("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.

   (2) Following the issuance discussed in note 1, 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.

   (3) The sole general partner of WP IX is 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"), is the sole member of WP IX LLC.
   Warburg Pincus & Co., a New York general partnership ("WP"), is the managing
   member of WPP LLC. Warburg Pincus LLC, a New York limited liability company
   ("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 (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 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.

   Mr. Janeway, who became a director of the Issuer on October 12, 2006, is a
   Partner of WP and a Member and Senior Advisor of WP LLC. As such, Mr. Janeway
   may be deemed to have an indirect pecuniary interest (within the meaning of
   Rule 16a-1 of the Act) in an indeterminate portion of the securities reported
   as beneficially owned by WP IX. Mr. Janeway disclaims beneficial ownership of
   such securities, except to the extent of any indirect pecuniary interest
   therein. Mr. Janeway does not directly own the Warrant or any shares of
   Preferred Stock. Mr. Janeway directly owns 3,896 shares of Common Stock.