Warren Buffett's conviction bet on Occidental Petroleum has inspired a legion of retail investors to follow suit. Ever since Berkshire Hathaway initially revealed a $5 billion stake in the oil giant, the stock has witnessed a massive 16.5-time increase in average daily net flows from retail investors — from $500,000 per day to $8.25 million a day, according to data from VandaTrack. "The Warren Buffett effect – Occidental Petroleum is now a popular retail stock," analysts from VandaTrack said in a note Wednesday. The "Oracle of Omaha" has been steadily adding to his Occidental stake since March, giving Berkshire a 19.4% Occidental stake worth about $10.9 billion. Occidental has been the best-performing stock in the S & P 500 this year, up about 113% so far on the back of surging oil prices. Berkshire also owns $10 billion of Occidental preferred stock, and has warrants to buy another 83.9 million common shares for $5 billion, or $59.62 each. The warrants were obtained as part of the company's 2019 deal that helped finance Occidental's purchase of Anadarko . The retail interest sparked by Buffett may seem ironic to some as the legendary investor has long been critical of speculative trading by small investors, comparing the stock market to a casino. In fact, during Berkshire's annual meeting at the end of April, Buffett said the volatility sparked by the heightened trading activity from retail investors enabled him in a two-week period to buy 14% of Occidental. "Essentially, this is a gambling parlor," Buffett told shareholders at the meeting. "And the people that were making money were people that worked with gamblers." Buffett also revealed that he read through Occidental's annual report and gained confidence in the company's growth and its leadership. "What Vicki Hollub was saying made nothing but sense. And I decided that it was a good place to put Berkshire's money," Buffett said. "Vicki was saying what the company had gone through and where it was now and what they planned to do with the money."