Exhibit 99.1

OneSource Board of Directors Forms Special Committee to Evaluate
Strategic Options and Adopts Shareholder Rights Plan

    CONCORD, Mass.--(BUSINESS WIRE)--Oct. 6, 2003--OneSource
Information Services, Inc. (NASDAQ: ONES) announced today that its
Board of Directors has formed a special committee of outside
independent directors to evaluate OneSource's strategic options to
maximize shareholder value. The special committee has engaged Morgan
Stanley & Co. and Portico Capital Securities LLC to assist it in this
review. The special committee will review potential strategic options
available to the Company and the recent unsolicited letter from
ValueAct Capital L.P. expressing an interest in an acquisition of
OneSource. ValueAct currently holds approximately a 32% ownership
interest in OneSource, according to its most recent SEC filing.
    OneSource also announced today that its Board of Directors adopted
a Shareholders Rights Plan designed to enhance the Board's ability to
provide for fair and equal treatment for all OneSource shareholders.
The adoption of a Rights Plan is intended to guard against any
potential takeover tactics that are designed to gain control of
OneSource without paying all shareholders a full and fair value or are
otherwise not in the best interest of the shareholders of OneSource.
    Under the Plan, each common shareholder at the close of business
on October 6, 2003 will receive a dividend of one right for each share
of Common Stock held. Each right entitles the holder to purchase from
OneSource one one-thousandth of a share of a new series of
participating Preferred Stock at an initial purchase price of $32.50.
The rights will become exercisable and will detach from the Common
Stock a specified period of time after any person has become the
beneficial owner of 15% or more of OneSource Common Stock or commenced
a tender or exchange offer which, if consummated, would result in any
person becoming the beneficial owner of 15% or more of the Common
Stock.
    If any person becomes the beneficial owner of 15% or more of
OneSource Common Stock, each right will entitle the holder, other than
the acquiring person, to purchase for a number of shares of capital
stock of OneSource having a value of twice the purchase price.
    If, following an acquisition of 15% or more of OneSource Common
Stock, OneSource is involved in certain mergers or other business
combinations or sells or transfers more than 50% of its assets or
earning power, each right will entitle the holder to purchase for the
purchase price common stock of the other party to such transaction
having a value of twice the purchase price.
    At any time after a person has acquired 15% or more (but before
any person has acquired more than 50%) of the Company's Common Stock,
OneSource may exchange all or part of the rights for shares of Common
Stock at an exchange ratio of one share of Common Stock per right.
    The Plan "grandfathers" ValueAct and its affiliates as long as
they do not acquire beneficial ownership of more than 35% of the
Common Stock.
    OneSource may redeem the rights at a price of $0.001 per right at
any time prior to the time that any person becomes the beneficial
owner of 15% or more of its Common Stock. The rights will expire on
October 6, 2013, unless earlier exchanged

    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 is headquartered in
Concord, MA, with offices located in North America, Europe, and the
Pacific Rim. Company and product information are available at
www.onesource.com.

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