NEW YORK ( TheStreet) -- Given the mix of winners and losers we have seen during the opening weeks of earnings season, it has likely been difficult for many stock pickers to avoid navigating the markets without a setback. Even Warren Buffett has seen a blend of both strength and weakness from the companies in his legendary portfolio.This week has been an important one for fans of the Oracle of Omaha. Over the past few days, some of the largest names in the Berkshire Hathaway ( BRK.A) stock portfolio have reported their earnings over the past quarter and provided insight into the closing months of the year. Of particular importance were Coca-Cola ( KO), Wells Fargo ( WFC) and American Express ( AXP), which represent the three largest slices of the portfolio. Buffett's stock portfolio casts a wide net across the broad market spectrum, offering exposure to financials, industrials, consumer goods, energy and other sectors. From an individual holdings perspective, however, the lineup is notably concentrated. Together KO, WFC, and AXP represent nearly 60% of the total assets. >>View Warren Buffett's Portfolio Swirling macroeconomic turbulence appears to have had only a limited effect on consumer demand for soft drinks over the past few months. Over the most recent three-month period, Coca-Cola reported an earnings growth of more than 8%. A Wall Street Journal report notes that, excluding charges including restructuring costs, the company was able to outpace analyst estimates. Despite this strength, the firm recognized that the road ahead is not entirely smooth as continued global economic turmoil and rising commodity costs are among the challenges they face. Berkshire's No. 3 holding, American Express, also fared favorably over the past three months, beating forecasts. Company executives pointed to consumer resilience as a major source of strength for the credit card giant over the quarter. In his statement included in the company's earnings press release, CEO Kenneth Chenault noted that card-member spending jumped 16% to a record level. Looking ahead, the company appears cautiously optimistic. Economic issues remain a cause for concern. However, Chenault mentions that AXP has taken a number of steps that have improved its competitiveness.