Key TakeawaysOccidental Petroleum shares are in focus on Monday after a regulatory filing released late Friday revealed that Berkshire Hathaway had increased its stake in the energy producer.The conglomerate purchased 2.6 million shares of Occidental Petroleum between Wednesday and Friday last week, taking its total stake in the company to 250.6 million shares valued at nearly $15 billion based on Friday’s $59.48 closing price.Occidental Petroleum shares find support at $56 from a trading range's lower tren ...