Transocean (RIG -1.6%) shares tumble after a downgrade from S&P Equity Research, based...

|By:, SA News Editor

Transocean (RIG -1.6%) shares tumble after a downgrade from S&P Equity Research, based in part on the sinking of the company's rig in the Gulf of Mexico. BP (BP -2.8%), who was leasing the rig and is responsible for cleaning up the mess, says it could take "several months" to stop the resulting oil spill.