Even as it faces $50 billion in potential liabilities from the worst U.S. offshore oil spill, BP Plc (BP/) is leading the effort to extract crude from deep below the sea, a place as extreme and inhospitable as the surface of Mars. BP, Chevron Corp. and Royal Dutch Shell Plc (RDSA) are among companies developing a new generation of oilfield technology to reach through more than seven miles of water and rock, where temperatures can reach 400 degrees Fahrenheit (200 degrees Celsius) and the pressure hits 20,000 pounds per square inch — and to do it safely. The conditions are more challenging than BP’s Macondo well in the Gulf of Mexico , where a 2010 rig explosion killed 11 people and caused a spill that fouled hundreds of miles of coastline. The companies are seeking to tap into $1 trillion in reserves offshore, where a major discovery can produce […]