A total of 56 oil and gas companies have issued $99.3 billion of debt in U.S. markets since the Federal Reserve began its bailout of corporate debt markets in late March. Some said they might fail without the fresh financing.• Of the 122 new bond issuances reviewed, 93 will be used at least in part to pay down or refinance a specifically named existing debt such as commercial paper, revolving credit lines, or other bonds. At least 15 companies are issuing new bonds to replace existing bonds that had higher coupon rates.