Exhibit 99.1

OneSource Receives Letter from ValueAct Capital

    CONCORD, Mass.--(BUSINESS WIRE)--Feb. 9, 2004--OneSource
Information Services, Inc. (NASDAQ: ONES), a leading provider of
business information products and services, today announced that it
has received a letter from ValueAct Capital indicating that it was
prepared to offer to acquire all of the outstanding shares of
OneSource at a cash price of $8.10 per share on the terms and
conditions contained in a merger agreement enclosed with the letter.
The special committee of the board of directors of OneSource is
reviewing the proposal in order to determine the course of action
which will serve the best interests of all stockholders.
    On October 3, 2003, OneSource announced that it had received an
unsolicited letter from ValueAct Capital expressing its interest in
acquiring OneSource's business. OneSource's board of directors
subsequently formed a special committee of outside independent
directors to evaluate OneSource's strategic options to maximize
shareholder value. The special committee engaged Morgan Stanley & Co.
and Portico Capital Securities LLC to assist it in this review. On
January 13, 2004, and February 9, 2004, ValueAct amended its Schedule
13D concerning its interest in acquiring OneSource's business.
ValueAct currently holds approximately a 32% ownership interest in
OneSource.

    About OneSource Information Services, Inc.

    OneSource, a recognized leader in business information solutions,
delivers unparalleled company, executive, and industry intelligence
that make business professionals more effective and productive in
completing their critical daily tasks. OneSource products and services
support a company's vital business processes including serving their
customers, finding and leveraging new opportunities, and managing
suppliers and partners.
    OneSource is headquartered in Concord, MA, with offices located in
North America, Europe, and the Pacific Rim. Product information is
available at www.onesource.com. Customers include Bank One, Chubb,
Citigroup, Cisco, Deloitte & Touche, HP, i2 Technologies, Orange,
Royal & SunAlliance, SAS Institute, and Sun Microsystems.

    CONTACT: OneSource Information Services, Inc.
             Roy Landon, 978-318-4377
             Roy_Landon@onesource.com