 The spill occurred because the pipe froze.Although sensors provided alarms of cold temperatures, BP employees testified that operators didn't use the cold alarms as a measure of flow, but rather as a measurement of the mixture of oil, gas, and water.In November 2010 BP's federal probation officer filed suit to revoke BP's probation stemming from the guilty plea for the 2006 spill, which could have led to further penalties for the 2006 spill, on the grounds that the 2009 Lisburne spill showed that BP was still negligent.