Salesforce for sale? The buyer list is very small

Oracle front-runner to buy Salesforce?
VIDEO6:1006:10 CEO: Focused on stakeholders
Who will buy Salesforce?
VIDEO1:5101:51 could be biggest tech deal of all time is a takeover target, according to a new report from Bloomberg. If true, the list of potential buyers is awfully small.

With a stock market capitalization of almost $49 billion after an 11 percent surge on the news, the only U.S. Internet and software companies that are valued higher are—in descending order—Microsoft, Google, Facebook, Oracle and IBM. All are worth between $171 billion and $399 billion.

Expanding internationally, that list includes China's Tencent, Germany's SAP and SoftBank out of Japan.

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Considering Salesforce's growth, which has exceeded 30 percent for four straight years, shareholders would surely demand a premium to the stock's current $75 price, requiring any buyer to spend an historically large sum of cash and stock. According to Bloomberg, even at $44 billion, it would be the largest acquisition ever for a software business.

Microsoft tried to buy Yahoo in 2008 for close to $45 billion, but that hostile effort notoriously failed.

Salesforce CEO Marc Benioff, who started the company in 1999 after a career at Oracle, declined to comment to CNBC. He did offer up a tweet Wednesday tied to the Microsoft Build conference.