The boom years left the US oil industry deep in debt. The 60 leading US independent oil and gas companies have total net debt of $206bn, from about $100bn at the end of 2006. As of September, about a dozen had debts that were more than 20 times their earnings before interest, tax, depreciation and amortisation. Worries about the health of these companies have been rising. A Bank of America Merrill Lynch index of high-yield energy bonds, which includes many indebted oil companies, has an average yield of more than 19%. Almost a third of the 155 US oil and...