Shares of Hess Corp. /zigman2/quotes/203832174/composite HES -2.13% slumped 5.7% and Occidental Petroleum Corp. /zigman2/quotes/207018272/composite OXY +0.98% dropped 3.6% in premarket trading Monday, as crude oil prices took another dive and oil driller Diamond Offshore Drilling Inc. declared bankruptcy. Continuous crude oil futures /zigman2/quotes/209723049/delayed CL00 -0.13% tumbled 22.6% in early trading amid continued demand and supply concerns, putting them on course to snap a three-day win streak in which they soared 31%. Meanwhile, Diamond had disclosed that Hess was its biggest customer in 2019, accounting for 28.9% of its annual revenue, while Occidental was its second-biggest customer at 20.6%. Among it's other biggest customers, the U.S.-listed shares of Petroleo Brasileiro S.A. /zigman2/quotes/200745132/composite PBR -0.10% rose 3.4% and BP PLC /zigman2/quotes/207305210/composite BP -1.30% gained 0.4%. Diamond Offshore said it had sufficient capital to fund operations during its bankruptcy reorganization. Diamond's stock plummeted 61% before being halted for news. Futures /zigman2/quotes/209948968/delayed ES00 +0.05% for the S&P 500 /zigman2/quotes/210599714/realtime SPX -2.57% rose 1.2%.