Check out the companies making the biggest moves premarket: Occidental Petroleum , Berkshire Hathaway — Occidental gained around 1% after Berkshire Hathaway announced it was buying the oil company's petrochemical division, OxyChem, for nearly $10 billion in cash . Class B shares of Berkshire Hathaway slipped about 0.2%. Fair Isaac — The stock rallied 19% after the company unveiled a system that allows mortgage lenders direct access to FICO scores. Credit bureaus Transunion and Equifax shed 11% each. Curbline Properties — The real estate trust rose more than 2% after it authorized a share repurchase program of up to $250 million. Celanese — The materials company rose more than 2% after Citi upgraded the stock to buy from neutral. "Despite the sluggish macro backdrop, we see continued self-help levers supporting some earnings growth into next year and divestitures helping to clean up the balance sheet," the bank said. Lithium Americas — Shares fell roughly 4% after a Canaccord Genuity downgrade to sell from speculative buy due to the likely limited benefits of the lithium company's recently revised loan with the U.S. Department of Energy. "We believe that the recent run-up in the stock price is overdone and does not accurately reflect the valuation implications of the revised deal with the DOE," Canaccord said in a note. Western Digital — Shares popped nearly 5%, adding to their 8.8% rally from the previous session. Nikkei reported, citing CEO Irving Tan, that the data storage company will invest $1 billion in Japan over the next half-decade. Bloom Energy — Mizuho downgraded the energy company to neutral from buy, pushing the stock down about 2%. The Wall Street firm said Bloom is limited by its internal production capacity and the stock is poised for a pullback following a 254% rally in the third quarter. — CNBC's Alex Harring, Liz Napolitano and Yun Li contributed reporting.
