Despite being a net seller of stocks to the tune of $166 billion over the last eight quarters, there are two premier stocks the Oracle of Omaha can't stop buying.

Warren Buffett is stockpiling cash. His Berkshire Hathaway holding company continued to sell more than it bought in the third quarter when it offloaded a quarter of its stake in Apple, regulatory filings revealed Thursday.

The beloved consumer brand recently purchased by the Oracle of Omaha has skyrocketed by roughly 7,000% since its public debut 20 years ago.

There is one stock he has never sold since buying in 1991, though: American Express ( AXP -0.20%). Buffett owns over 20% of the credit card issuer and bank, making it the second-largest position in the Berkshire Hathaway portfolio. The position trades at a value of $40 billion as of this writing.