MOEX, a unit of Japanese trading house Mitsui & Co <8031.T>, and partner in BP Plc's doomed Macondo well has agreed to pay the UK oil major $1.1 billion toward the cost of the Gulf of Mexico oil spill.

MOEX had a 10 percent stake in the well and was liable for a commensurate portion of the costs, which BP estimated at $41 billion, including fines.

BP said in a statement on Friday the settlement excludes punitive damages -- which BP does not believe will be payable -- and fines, which analysts believe make up about $4 billion of BP's estimate, suggesting the Japanese company is paying less than a third of its potential liability.

BP called on its other partner in the well, Anadarko Petroleum , to also settle. Anadarko has a 25 percent stake in the well, so if it settled on the same basis as MOEX, it could face a bill of almost $2.7 billion.

MOEX had previously refused to pay BP any money related to the disaster, saying it was due to BP's negligence. MOEX has now joined BP in blaming the accident principally on Transocean , the company which BP hired to drill the well, under BP's instruction.

The Commission appointed by President Barack Obama to investigate the rig blast which led to the United States's worst ever spill said BP was responsible for most of the bad decisions on the rig.

Mitsui said it had no plan to change its forecast net profit or dividend in 2011/2012 after the settlement.