Two years ago, Warren Buffett told Berkshire Hathaway Inc. shareholders he was on the lookout for major acquisitions, as part of his unending effort to profitably employ the buckets of cash his company collects every month.

Since then, however, the billionaire investor has fired what he called his 'elephant gun' just twice. Berkshire in February said it would join with a Brazilian investment firm to buy ketchup maker H.J. Heinz Co. for $23.4 billion. In 2011, Berkshire bought engine lubricant-maker Lubrizol Corp. for $9 billion.

The challenge of finding a big target at the right price will again be on investors' minds when Berkshire files its annual report Friday afternoon. The report includes the shareholder letter penned by the 82-year-old Mr. Buffett, which over the years has been the source of many of the bon mots for which the Omaha, Neb., company's chairman and chief executive is known.

There have been large stock purchases, such as a 2011 acquisition of $10.7 billion in International Business Machines Corp. stock, and smaller recent deals such as the purchase of Oriental Trading Co. for an undisclosed price.

But largely absent have been the multibillion-dollar takeovers that over time transformed Berkshire from a widely followed stock portfolio to a highly profitable conglomerate valued at over $250 billion. Before Heinz, the most recent megadeal was the 2010 purchase of railroad Burlington Northern Santa Fe Corp. for $26.3 billion.

It isn't that Mr. Buffett hasn't been searching. Last year, his company participated in discussions to buy NYSE Euronext, the parent of the New York Stock Exchange. The two sides didn't agree on price, and NYSE eventually announced an agreement to sell itself to IntercontinentalExchange Inc. for $8.2 billion.

In May, Mr. Buffett said he walked away from a potential $22 billion deal because of a difference in price, and because it would have meant selling some stock from Berkshire's portfolio to help pay for the acquisition.

The company had $47.8 billion in cash and cash equivalents as of Sept. 30, far in excess of the $20 billion or so Mr. Buffett has said he would like to hold on Berkshire's balance sheet. Berkshire is spending $12 billion in cash for the Heinz deal. The company can also sell securities it owns to pay for large deals.

One likely reason is that Mr. Buffett simply hasn't found a company he likes enough at a price that is right. 'Often, businesses are priced ridiculously high against what can likely be earned from investments in stocks and bonds,' he said in his 2011 letter.

Investors are also likely to parse the letter for any comments on Berkshire shares. Mr. Buffett has said he would not use Berkshire shares to pay for deals unless the shares are fairly priced. Berkshire's Class A shares have risen around 27% in the past 12 months and recently hit a record high.

In December, Berkshire bought $1.2 billion of its own Class A shares from the estate of a 'longtime shareholder.' The move showed that Mr. Buffett believed Berkshire shares were undervalued at the time, and spending cash on repurchasing shares was a better use of capital than acquisitions.

Besides discussing Berkshire's recent performance, Mr. Buffett's letter Friday is likely to detail a change to the format of the company's annual shareholders' meeting, which draws over 30,000 individuals to Omaha each spring.

Last year, Mr. Buffett had three Wall Street analysts join shareholders and a panel of journalists in questioning him and his business partner Charlie Munger. Mr. Buffett said his goal was to broaden the conversation and field more questions about Berkshire's operations.

Of the three insurance analysts who questioned Mr. Buffett at last year's meeting, one will be on the panel this year.

Mr. Buffett may fill one of the other two spots with an analyst who covers industrial companies, reflecting how Berkshire now derives the bulk of its profits from nonfinancial businesses such as railroads and utilities, according to people familiar with the situation.

It is unclear who will fill the third spot, but some investors think it may be an individual with a contrarian view of Berkshire. Mr. Buffett declined to discuss the change, saying he would explain it in his letter.