Oracle Corp Chief Executive Larry Ellison said Sun Microsystems Inc is losing about $100 million a month as European regulators delay approving his company's $7 billion purchase of the struggling hardware maker.

The longer this takes, the more money Sun is going to lose, Ellison said on Monday evening during a dinner at one of Silicon Valley's most prominent speaker's forums, the Churchill Club.

Sun's revenue has tumbled since April when Oracle agreed to buy the world's No. 4 computer server maker in April as rivals IBM and Hewlett-Packard Co have poached customers amid uncertainty about its future.

Oracle has pledged to boost investment on development of Sun's products, but the hardware company has cut spending prior to the deal's closing as sales have plunged. Last month it reported a quarterly loss of $147 million.

Ellison, the world's fourth-richest man according to Forbes, said he expects the deal will eventually be cleared by European regulators as it was in the United States, without any conditions.

The European Commission is conducting an in-depth probe into whether the competition would be stifled by the combination of Oracle's database, the world's top seller, and Sun's MySQL database, which is widely used to run popular websites.

Legal experts have said Oracle may need to make concessions, including the divestiture of the MySQL software business, and that it is unclear how long European approval would take.

European regulators have until January 19, the deadline set by the Commission, the competition watchdog of the 27-country European Union. That would put Oracle months behind its original plan for closing the deal by the end of August.

(Reporting by Alexei Oreskovic in San Jose and Jim Finkle in Boston; Editing by Anshuman Daga)