Eloqua buy represents the latest move in Oracle's "marketing cloud" acquisitions duel with Salesforce.com.

Oracle is buying marketing automation software specialist Eloqua, the companies announced Thursday.

This is the latest in a series of social, Internet marketing and customer experience software purchases by Oracle.

According to the Wall Street Journal, Oracle offered $23.50 for each Eloqua share, a 31% premium over Wednesday's closing price. That makes this roughly an $810 million purchase. The deal is expected to close in the first half of 2013. Eloqua makes marketing automation software that can be used to manage email campaigns, landing pages and other methods of promotion and sales lead capture. It is particularly focused on conducting business-to-business marketing campaigns.

"Modern marketing practices are driving revenue growth and is a critical area of investment for companies today," Thomas Kurian, executive VP, Oracle Development, said in a press release. "Eloqua's leading marketing automation cloud will become the centerpiece of the Oracle Marketing Cloud."

Interestingly, Oracle seems to be adopting the nomenclature used by Salesforce.com, which now refers to the combination of the Radian6 social media monitoring and analytics and Buddy Media social media marketing units as the Salesforce Marketing Cloud. Radian6 and Buddy Media are two of the companies Salesforce acquired to round out its social software portfolio, and Oracle has been countering with acquisitions of its own of companies like Involver and Vitrue.

For Eloqua, one complication of being owned by Oracle is that Eloqua's marketing automation software is commonly used as a companion to Salesforce.com CRM, supporting business-to-business marketing campaigns that feed leads to salespeople. Eloqua is also embedding Chatter collaboration throughout its product, partly as a way of encouraging marketing and sales to work together. So Salesforce would have seemed a much more likely buyer for Eloqua than Oracle.

The Salesforce Marketing Cloud offering has so far been focused on social media marketing. That's one reason Eloqua executives have maintained during the past year that they didn't see it as a threat, and called it more complementary than competitive.

Now, Oracle seems to have decided it can't stop at social but must try to dominate digital marketing software as a whole.

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