BOSTON ( TheStreet) -- Warren Buffett's Berkshire Hathaway ( BRK.B) made only two trades in the first quarter: initiating a small stake in credit-card company MasterCard ( MA) and trimming its big stake in oil company ConocoPhillips ( COP).It's the second quarter in a row of little activity for the investment company run by the man dubbed the Oracle of Omaha for the trading prowess that helped him build an estimated net worth of $50 billion over half a century. In the first quarter, former hedge fund manager Todd Combs started working at Berkshire, managing part of the portfolio, as the 80-year-old billionaire selects a succession team. Berkshire Hathaway's 26-stock investment portfolio was valued at $53.6 billion as of March 31, up $1 billion, or 2%, from the end of 2010, according to a Securities and Exchange Commission report that the hedge fund filed late Monday. Buffett isn't required to publish foreign holdings. The benchmark S&P 500 Index rose 5.4% in the first quarter.
Berkshire Hathaway's only buy during the first quarter was MasterCard, which is up 25% this year and 21% over the past 12 months. Its value in the fund was $54 million at the end of the first quarter, and it made up 0.1% of the portfolio. Combs, the newly arrived investment manager, specialized in financial holdings, and he may have selected that stock. MasterCard manages a group of global payment card brands, including MasterCard, Maestro and Cirrus, which it licenses to financial institutions that issue cards to their customers. The firm acts as the payment processor by facilitating the authorization, clearing and settlement of transactions on its proprietary networks. MasterCard's profit jumped 24% to $562 million from $455 million a year earlier. Revenue rose 15% to $1.5 billion. MasterCard's larger rival, Visa ( V), also reported a 24% profit increase, to $881 million, as well as the same percentage increase in revenue, to $2.25 billion. Visa's shares are up 14% this year, though, trailing MasterCard's 25% gain. Berkshire's filing with the SEC said "confidential information has been omitted" and "filed separately with the Commission," suggesting the company may be building up a new stake and is keeping it under wraps, as is allowed by the regulator. The current quarter's filing, due mid-August, may reveal that company.