Warren Buffett's holding company Berkshire Hathaway has increased its stake in Houston, U.S.-based ... [+] energy company Occidental Petroleum to 28.8%. (Photo: Nati Harnik)Copyright 2018 The Associated Press. All rights reserved. If you had bought shares in Occidental Petroleum (NYSE: OXY) in June last year, the company's share price was lurking just south of the $60 mark at around $57. Twelve months down the road, the price is currently just north of $60 at around $61.It points to an annualized gain of 7% ...