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.

Plenty of big-time investors have made a name for themselves over the years, but arguably none have become as big of a household name as Warren Buffett. Thanks to personal achievements and the success of his company,

There is one stock he has never sold since buying in 1991, though: American Express (NYSE: AXP). 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.