Lee Tillman, chief executive officer of Marathon Oil Corp., told investors last month that the company was sitting on the equivalent of 4.3 billion barrels in its U.S. shale acreage. That number was 5.5 times higher than the proved reserves Marathon reported to federal regulators. Such discrepancies are rife in the U.S. shale industry. Drillers use bigger forecasts to sell the hydraulic fracturing boom to investors and to persuade lawmakers to lift the 39-year-old ban on crude exports. Sixty-two of 73 U.S. shale drillers reported one estimate in mandatory filings with the Securities and Exchange Commission while citing higher potential figures to the public, according to data compiled by Bloomberg. Pioneer Natural Resources (PXD) Co.’s estimate was 13 times higher. Goodrich Petroleum Corp.’s was 19 times. For Rice Energy Inc., […]