Warren Buffett faces the dilemma of having to buy enormous positions in companies in order to generate returns that make any difference at his insurance behemoth, Berkshire Hathaway (BRK.A )(BRK.B ). In his early days, he required a compound annual future earnings growth rate of 10% before he would buy a company, and had many fitting that profile to choose from. Now, size has limited his stock universe somewhat.

Buffett’s portfolio stalwarts include companies that continue healthy growth, in spite of size: American Express (AXP ), Coca-Cola (KO ), IBM (IBM ) and Wells Fargo (WFC ). These companies have the following five-year EBITDA per share growth rates, respectively: 19%, 8.8%, 9.5% and 33%. In 2012, Buffett added to his positions in Wells Fargo and IBM, and expects continued growth at all four. In his annual shareholder letter he wrote:

The earnings that the four companies retain are often used for repurchases – which enhance our share of future earnings – and also for funding business opportunities that are usually advantageous. Over time we expect substantially greater earnings from these four investees. If we are correct, dividends to Berkshire will increase and, even more important, so will our unrealized capital gains (which, for the four, totaled $26.7 billion at yearend).

Other companies within his portfolio are displaying rapid earnings growth, and Buffett (or one of his new portfolio managers – Ted Weschler or Todd Combs) has been increasing his positions in them, though they are still smaller positions. The companies are: National Oilwell Varco Inc. (NOV ) and Suncor Energy Inc. (SU ). Here is the complete portfolio of Warren Buffett. Also check out:

National Oilwell Varco Inc. (NOV )

Buffett began buying National Oilwell Varco in the second quarter of 2012, and has been buying shares each quarter since. As of June 30, 2013, he owns 8.88 million shares, with an average gain of 11%.

The Forbes E-book On Warren Buffett The $59 Billion Philanthropist. chronicling 50 years of Buffett’s investment savvy and unprecedented giving, is available now for download.

Oil and gas exploration company National Oilwell has a 10-year EBITDA growth rate of 28.4% — the highest growth rate company in his portfolio. Though the company’s average growth has slowed to 5.4% over the past five years, in 2012, it increased 18.9% from the previous year.

National Oilwell Varco designs and sells components for the oil and gas drilling and production industry. In the second quarter, it enjoyed significant demand that led to record backlog of capital equipment and international growth, in spite of weakness in Canada and the U.S. Revenues increased 6% year over year to $5.6 billion and earnings increased to $531 million from $502 million in the prior-year quarter.

Management also decided to return more of its earnings to shareholders. The company doubled its regular dividend during the quarter, to $0.26 per share from $0.13 per share.

Buffett established a position in Suncor Energy Inc. in the second quarter of 2013, buying 17,769,457 shares at an average price of $30. He has an average gain of 17% on the holding.

Suncor has an 11.4% EBITDA per share growth rate for the past 10 years. Growth has actually increased at the company more recently – its five-year growth rate is 16.5%.

Suncor is also related to the oil and gas industry. An integrated energy company, it develops and produces conventional oil and natural gas in Western Canada, the East Coast of Canada and internationally. The company also has a lubricants business, wind power projects and a biofuels plant, along with several other oil plays.