Siebel Systems to Webcast Select Siebel User Week Sessions

    Business Editors/Technology Writers

    SAN MATEO, Calif.--(BUSINESS WIRE)--April 15, 2005--Siebel Systems, Inc. (Nasdaq:SEBL), a leading provider of business applications software, today announced it will provide audio or video Webcasts of select conference sessions from Siebel User Week 2005, to be held April 17-20 at the Centre Convencions Internacional Barcelona (CCIB) in Barcelona, Spain.

MONDAY, APRIL 18, 2005

9:00 a.m.-11:00 a.m. Central Europe Time (CET)--Welcome address by Neil Morgan, Vice President, European Marketing, Siebel Systems and keynote addresses by George T. Shaheen, CEO, Siebel Systems and Rik Op den Brouw, Senior Executive Vice President of Group ICT, Rabobank

To access the live Webcast and replay:

http://a59.g.akamai.net/f/59/7221/1m/web-ivt.mediaplatform.com/mp/4000 /5595/5596/14275/Lobby/default.htm

The replay will be available until May 18, 2005.

11:30 a.m.-12:30 p.m. CET--Siebel executive Q&A featuring George T. Shaheen and members of Siebel Systems' executive management team

To access the audioconference: ------------------------------ AUSTRALIA Toll Free Number: 1-800-004-980 AUSTRALIA Toll Number: +61-2-8211-1385 AUSTRIA Toll Number: +43-1-92-89-655 BELGIUM Toll Number: +32-2-402-3407 FINLAND Toll Number: +358-106-33-163 FRANCE Toll Number: +33-1-70-75-00-02 GERMANY Toll Number: +49-69-2222-52100 GREECE Toll Number: +30-80-1-100-0638 HONG KONG Toll Number: +852-2286-5631 INDONESIA Toll Free Number: 001-803-011-3494 IRELAND Toll Free Number: 1-800-931-767 IRELAND Toll Number: +353-1-246-0034 ISRAEL Toll Free Number: 1-800-9213917 ITALY Toll Free Number: 800-906-410 ITALY Toll Number: +39-02-3600-0324 JAPAN Toll Free Number: 00531-12-1251 JAPAN Toll Number: +81-3-5539-5153 LUXEMBOURG Toll Number: +352-27-000-1313 MALAYSIA Toll Free Number: 1-800-80-8112 NETHERLANDS Toll Free Number: 0800-023-4478 NETHERLANDS Toll Number: +31-20-710-0075 NEW ZEALAND Toll Free Number: 0800-443-817 NORWAY Toll Free Number: 800-11794 NORWAY Toll Number: +47-21-59-00-13 POLAND Toll Free Number: 00-800-1210055 PORTUGAL Toll Free Number: 8008-12167 SINGAPORE Toll Free Number: 800-120-4055 SINGAPORE Toll Number: +65-6883-9196 SOUTH AFRICA Toll Free Number: 080-09-93382 SOUTH KOREA Toll Free Number: 00798-14800-6319 SPAIN Toll Free Number: 800-099-269 SPAIN Toll Number: +34-91-414-15-45 SWEDEN Toll Free Number: 0200-887-605 SWEDEN Toll Number: +46-8-566-10-783 SWITZERLAND Toll Free Number: 0800-000-056 SWITZERLAND Toll Number: +41-44-580-7807 TAIWAN Toll Free Number: 00801-137-561 TAIWAN Toll Number: +886-2-2795-7345 THAILAND Toll Free Number: 001-800-1206-65084 UNITED KINGDOM Toll Free Number: 0800-018-0764 UNITED KINGDOM Toll Number: +44-20-7019-0810 USA Toll Free Number: 877-951-7311 USA Toll Number: +1-210-795-0466

Passcode: PRESS

For security reasons, the passcode and the leader's name will be required to join the call.

To join the netconference: https://www.mymeetings.com/nc/join/ Conference Number: PG5968247 Passcode: PRESS

To join the event directly: https://www.mymeetings.com/nc/join.php?i=PG5968247&p=PRESS&t=c

To access the net replay: https://www.mymeetings.com/nc/join.php?i=PG5968247&p=PRESS&t=r

The replay will be available until May 18, 2005.

TUESDAY, APRIL 19, 2005

9:00 a.m.-11:00 a.m. CET--Keynote addresses by David Schmaier, Executive Vice President, Siebel Systems and John Heveran, Vice President, Information Technology, MCI

To access the live Webcast and replay: http://a59.g.akamai.net/f/59/7221/1m/web-ivt.mediaplatform.com/mp/4000 /5595/5596/14283/Lobby/default.htm

The replay will be available until May 19, 2005.

11:15 a.m.-12:15 p.m.--Siebel customer panel hosted by Neil Weston, President, EMEA, Siebel Systems

To access the audioconference: ----------------------------- AUSTRALIA Toll Free Number: 1-800-004-980 AUSTRALIA Toll Number: +61-2-8211-1385 AUSTRIA Toll Number: +43-1-92-89-655 BELGIUM Toll Number: +32-2-402-3407 FINLAND Toll Number: +358-106-33-163 FRANCE Toll Number: +33-1-70-75-00-02 GERMANY Toll Number: +49-69-2222-52100 GREECE Toll Number: +30-80-1-100-0638 HONG KONG Toll Number: +852-2286-5631 INDONESIA Toll Free Number: 001-803-011-3494 IRELAND Toll Free Number: 1800-931-767 IRELAND Toll Number: +353-1-246-0034 ISRAEL Toll Free Number: 1-800-9213917 ITALY Toll Free Number: 800-906-410 ITALY Toll Number: +39-02-3600-0324 JAPAN Toll Free Number: 00531-12-1251 JAPAN Toll Number: +81-3-5539-5153 LUXEMBOURG Toll Number: +352-27-000-1313 MALAYSIA Toll Free Number: 1-800-80-8112 NETHERLANDS Toll Free Number: 0800-023-4478 NETHERLANDS Toll Number: +31-20-710-0075 NEW ZEALAND Toll Free Number: 0800-443-817 NORWAY Toll Free Number: 800-11794 NORWAY Toll Number: +47-21-59-00-13 POLAND Toll Free Number: 00-800-1210055 PORTUGAL Toll Free Number: 8008-12167 SINGAPORE Toll Free Number: 800-120-4055 SINGAPORE Toll Number: +65-6883-9196 SOUTH AFRICA Toll Free Number: 080-09-93382 SOUTH KOREA Toll Free Number: 00798-14800-6319 SPAIN Toll Free Number: 800-099-269 SPAIN Toll Number: +34-91-414-15-45 SWEDEN Toll Free Number: 0200-887-605 SWEDEN Toll Number: +46-8-566-10-783 SWITZERLAND Toll Free Number: 0800-000-056 SWITZERLAND Toll Number: +41-44-580-7807 TAIWAN Toll Free Number: 00801-137-561 TAIWAN Toll Number: +886-2-2795-7345 THAILAND Toll Free Number: 001-800-1206-65084 UNITED KINGDOM Toll Free Number: 0800-018-0764 UNITED KINGDOM Toll Number: +44-20-7019-0810 USA Toll Free Number: 877-951-7311 USA Toll Number: +1-210-795-0466

Passcode: PRESS

For security reasons, the passcode and the leader's name will be required to join the call.

To join the netconference: https://www.mymeetings.com/nc/join/ Conference Number: PG5969062 Passcode: PRESS

To join the event directly: https://www.mymeetings.com/nc/join.php?i=PG5969062&p=PRESS&t=c

To access the net replay: https://www.mymeetings.com/nc/join.php?i=PG5969062&p=PRESS&t=r

The replay will be available until May 19, 2005.

WEDNESDAY, APRIL 20

9:00 a.m.-11:00 a.m. CET--Keynote addresses by Don Peppers, Founding Partner, Peppers & Rogers Group and Bruce Cleveland, Senior Vice President and General Manager, OnDemand and SMB, Siebel Systems

To access the Webcast and replay: http://a59.g.akamai.net/f/59/7221/1m/web-ivt.mediaplatform.com/mp/4000 /5595/5596/14284/Lobby/default.htm

The replay will be available until May 20, 2005.
    About Siebel Systems

    Siebel Systems, Inc. is a leading provider of business applications software, enabling corporations to sell to, market to, and serve customers across multiple channels and lines of business. With more than 4,000 customer deployments worldwide, Siebel Systems provides organizations with a proven set of industry-specific best practices, CRM applications, market-leading analytics products, and business processes, empowering them to consistently deliver superior customer experiences and establish more profitable customer relationships. Siebel Systems' sales and service facilities are located in more than 30 countries. For more information about Siebel Systems, Inc., please visit www.siebel.com.

    For more information on Siebel Systems solutions and services, please visit our Web site: CRM - http://www.siebel.com/crm; OnDemand Solutions - http://www.crmondemand.com; Industry CRM - http://www.siebel.com/industry-crm; Call Center & Service - http://www.siebel.com/call-center; Sales Force Automation - http://www.siebel.com/sales-force-automation; Marketing Automation - http://www.siebel.com/marketing-automation; Business Intelligence - http://www.siebel.com/business-intelligence; Integration Solutions - http://www.siebel.com/integration-solutions; CRM Services - http://www.siebel.com/crm-services.

    Except for the historical information contained herein, this press release contains forward-looking statements that involve risk or uncertainties. Future operating results of Siebel Systems may differ from the results discussed or forecasted in the forward-looking statements due to factors that include, but are not limited to, risks associated with customer relations, such as the availability of Siebel Systems' products and services, customer implementation of products and services, relationships with customers, third-party vendors and systems integrators, concentration of revenues in a relatively small number of customers, existence of errors or defects in products, ability to successfully manage growth, significant current and expected additional competition and the need to continue to expand product distribution and services offerings. Further information on potential factors that could affect the financial results of Siebel Systems are included in Siebel Systems' Annual Report on Form 10-K, Quarterly Reports on Form 10-Q and its other filings with the Securities and Exchange Commission, which are available at www.sec.gov. Siebel Systems assumes no obligation to update the information in this press release.

    NOTE: Due to their length, the Webcast URLs may need to be copied/pasted into your Internet browser's address field.

--30--MC/sf*

CONTACT: Siebel Systems, Inc. Cecilia Denny, 650-477-5861 cecilia.denny@siebel.com

KEYWORD: CALIFORNIA SPAIN INTERNATIONAL EUROPE INDUSTRY KEYWORD: HARDWARE SOFTWARE CONFERENCE CALLS SOURCE: Siebel Systems, Inc.

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