Souring energy loans quadrupled to $34.2 billion since 2014 as oil prices tumbled, according to a report released today by regulators led by the Federal Reserve. Loans deemed substandard, doubtful or a loss account for 12 percent of the banking industry’s $276.5 billion oil and gas portfolio, according to the report from the Fed, Federal Deposit Insurance Corp. and Office of the Comptroller of the Currency. The review is designed to assess the risk of $3.9 trillion in loans shared by multiple financial institutions. “Companies incurred significant debt to fund drilling programs, and their capital structures became unsustainable in the face of lower oil prices,” the regulators wrote in the report.