The oil company couldn't overcome the pressure of falling oil prices. Shares of Diamondback Energy (FANG 3.87%) slumped 11.6% in September, according to data provided by S&P Global Market Intelligence. Lower crude oil prices weighed on the oil company's stock price last month. That offset some positive news for the oil producer. Down despite some positive catalysts Crude oil prices continued to cool off last month. West Texas Intermediate (WTI), the primary U.S. oil price benchmark, fell 7.3% for the month, ...