Buffett, Berkshire's widely watched chairman and CEO, highlighted the industry's strength at this year's shareholders' meeting in Omaha.
"Payments are a huge deal worldwide," Buffett said when asked about the Warren Buffett Archive from CNBC to American Express. "And you have all sorts of clever people working on different ways to change the payment methods."
Berkshire portfolio managers Todd Combs and Ted Weschler made "significant" investments in Visa and Mastercard when the company had already bet on American Express. Buffett said the Amex stake did not stop him from having his portfolio managers buy others in the industry.
"I could have bought it [Visa and Mastercard] Besides, "said Buffett. If I had been as smart as Ted or Todd, I would have done that. "
Some of Berkshire's strongest performances over the past year came from Visa and Mastercard, which grew 24 percent and 30 percent year-on-year, respectively. American Express rose 6 percent over the same period.
Still, Buffett said American Express had "done a fabulous job" and said he "loves the fact" that they own 17 percent of the company.
"It is a company that has done a fantastic job in a highly competitive area where many people like to take their customers away from them," Buffett said. "International growth has accelerated, the penetration of small businesses is great, it's really a business."