Stone did not say which unit it would use, but the UK-listed driller currently has six of the units working inthe Gulf of Mexico.

The Ensco 8502 due to come off a contract with Nexenand LLOG in July.

The rig is currently on contract for a dayrate in the low $500s, according to an Ensco fleet status report, and drilling wells in LLOG's Delta House development.

The