The world's 5th richest person, Warren Buffett, cannot be considered an energy investor per se since his other investments dwarf what he has put into oil and gas stocks. Nevertheless, Buffet has seen his net worth decrease by $2.1B in the year-to-date to $105B. After a five-month hiatus, Buffett has resumed buying shares of Occidental Petroleum (NYSE:OXY). Earlier this month, Buffett's company spent $355 million on OXY stock in three days, raising its stake in the energy giant to 22.2%.