HOUSTON—Exxon Mobil Corp. signaled on Thursday that higher oil and gas prices would boost third-quarter earnings by as much as $1.5 billion over the second quarter. Natural gas prices in the United States have more than doubled this year and oil prices are up 52 percent as energy demand recovers from the COVID-19 pandemic. Exxon also has been cutting costs and laying off personnel following a historic loss in 2020. Lower costs coupled with the recent rebound in oil and gas have driven profit sharply higher. Natural gas prices should give the U.S. oil producer the largest increase in operating profit in the quarter, the company signaled in a corporate filing. Profit from natural could rise between $500 million—900 million this quarter over last, it said. U.S. natural gas prices were trading at almost $6 per million British Thermal units on Thursday. Healthier refining margins could add from $500 million …