Oracle has made an offer to buy middleware vendor BEA Systems.

Oracle said it had written to BEA's board of directors on Tuesday to make the offer, for US$17 per share, which represents a premium of 25 percent over BEA's closing share price on Thursday. The Wall Street Journal valued the offer at US$6.66 billion.

BEA was a pioneer in the market for Java application server software used to deploy business applications, competing with products like IBM's WebSphere. It has been rumored to be an acquisition target on numerous occasions but managed to retain its independence.

"This proposal is the culmination of repeated conversations with BEA's management over the last several years," said Oracle President Charles Phillips. "We look forward to completing a friendly transaction as soon as possible."

However, BEA executives were not quoted in the statement and there was no indication early Friday as to whether the company was open to being acquired.

Oracle said the acquisition would help it to beef up its own middleware suite, an important area for the company that is serving to link several families of business applications that it has acquired.

The company said it would protect the investments of BEA customers if the deal were to go ahead.

"Our continuing support commitment has been amply demonstrated with all of our previous acquisitions, including PeopleSoft and Siebel. BEA will be no different," Phillips said.

Oracle's Fusion middleware already includes many of the products BEA sells, including an application server, portal server and development tools, meaning the acquisition would create considerable overlap.

Stephen O'Grady, principal analyst with RedMonk, said Oracle's primary motive is likely the expansion and solidification of its presence in the middleware market.

"For all that BEA is not at the heights that it once was, it still owns solid accounts across global enterprises, and while Oracle obviously isn't lacking for presence in those accounts, BEA's middleware is often more highly regarded," O'Grady said.

BEA was an early leader in applications servers but saw its lead whittled down gradually by IBM and later by Oracle, which built up a strong middleware business itself. Oracle CEO Larry Ellison often liked to predict BEA's demise, but the company has managed to cling onto a respectable market share by developing new SOA and business process management technologies.

It has been under pressure of late, however, notably from the billionaire investor Carl Icahn, one of BEA's large shareholders. Icahn said last month that he would press for the sale of BEA, believing the business would find it hard to stay afloat as an independent company.

The deal would mark yet another big acquisition for Oracle, which is on an unprecedented buying spree that has netted it more than 30 software companies in the past three years. They include the applications vendors PeopleSoft, Siebel and JD Edwards, performance management vendor Hyperion Corp., and database vendors TimesTen and Innobase.

Ellison has said the acquisitions are designed to win the company new customers and increase its economies of scale so that it can invest heavily to become a leader in the applications market.

The deals have catapulted Oracle into second place behind SAP in the business applications market, although analysts question how Oracle can manage so many different product lines and integrate them under one roof.

Oracle indicated earlier this year that it would ease off the blockbuster acquisitions while it integrated the other companies it has bought. However, Ellison has always seemed to covet BEA, and he may feel that the unrest caused by Icahn has given him a chance to act.