Chief Executive Marc Benioff will make a high-profile speech at a conference held by arch rival Oracle Corp, giving him a rare chance to hawk his goods in hostile territory.

Both companies are vying for control of a $9-billion-a-year market for software that businesses use to manage sales, marketing and contacts with customers.

Billionaire Larry Ellison's Oracle is trailing Salesforce in the fastest-growing segment of that market -- programs that the software makers host at their own data centers and deliver to customers over the Internet. Analysts say that Oracle will announce new Web-based products at the conference, which begins on Sunday.

Technology researcher Gartner estimates that Web-based sales management software sales will more than double from $1.9 billion in 2008 to $4 billion in 2013.

Benioff will be joined on stage at San Francisco's Yerba Buena Center 757-seat Novellus Theater on Oct 13 by Dell Inc CEO Michael Dell, head of the computer maker that is one of Salesforce's biggest customers.

Oracle, the world's No. 3 software maker, disclosed Benioff's appearance on a website that lists the schedule for Oracle Open World conference, which runs Oct. 11-15.

Officials with Salesforce could not be reached to discuss Benioff's plans for the presentation, which is titled The best of both worlds: customer success in the cloud with Oracle and

It was unclear why Oracle allowed Benioff to speak at the conference -- in what will be the first time he has ever appeared on stage at the event.

Oracle spokeswoman Deborah Hellinger declined comment.

While Salesforce and other Oracle rivals such as IBM and SAP AG regularly participate in the conference, it is rare for Ellison to allow them to make high-profile speeches. Those sessions are reserved for Oracle's top executives and its closest business partners.

This year, some 400 companies that sell goods and services that work with Oracle's software will participate. They are vying for the attention of tens of thousands of customers who will be in attendance. and IBM are among some three dozen companies that are official sponsors of the Oracle conference. (Reporting by Jim Finkle; Editing by Tim Dobbyn)