Designated Filer: Janeway, William H.
Issuer & Ticker Symbol:   NYFIX, Inc. (NYFX)
Date of Event Requiring Statement: March 11, 2008


                                                                    Exhibit 99.1

                            Explanation of Responses:


(1) Following the purchases on March 11 and 12, 2008 of the common stock, par
value $0.001 per share ("Common Stock") of NYFIX, Inc. (the "Issuer"), Warburg
Pincus Private Equity IX, L.P., a Delaware limited partnership ("WP IX") is the
direct record owner of 2,800,227 shares of Common Stock and 1,500,000 shares of
the Series B Voting Convertible Preferred Stock (the "Preferred Stock"), which
is convertible into 15,000,000 shares of Common Stock. 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; and 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 W P IX. Each of WP, WP
LLC, WPP LLC, WP IX LLC, Mr. Kaye and Mr. Landy disclaim beneficial ownership of
all shares of the Common Stock and Preferred Stock beneficially owned by WP IX,
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 any shares of Common Stock or Preferred Stock.

(2) 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.

(3) 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.

(4) 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.

(5) 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.

(6) 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 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 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 the Warrant reported as beneficially owned by WP IX. Mr.
Janeway disclaims beneficial ownership of the Warrant, except to the extent of
any indirect pecuniary interest therein. Mr. Janeway does not directly own the
Warrant.