New York (CNN Business) Investing legend Warren Buffett is looking for an "elephant" of a deal to help Berkshire Hathaway's portfolio fly higher.

The Oracle of Omaha wrote in his latest annual shareholder letter in February that he's itching to make a sizable acquisition .

Buffett conceded that the likelihood of an imminent deal is remote because the stock market rally has made most takeover targets prohibitively expensive.

"Prices are sky-high for businesses possessing decent long-term prospects," he wrote, adding that this "disappointing reality" will likely mean that Berkshire will add to its pile of cash.

"We continue, nevertheless, to hope for an elephant-sized acquisition," Buffett said.

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