Fuel tanks on the grounded drilling rig on Lewis have been breached, releasing an unknown amount of diesel oil into the sea.
It is understood Transocean’s Winner rig, which was blown ashore earlier this week at Dalmore Beach, was carrying 280 metric tonnes of oil.
The Maritime and Coastguard Agency said two out of the four tanks holding oil appear to have been damaged.
However, there are no signs of oil around the rig or on the nearby beach.
So far, bad weather has stopped salvage teams from getting to the rig.
The MCA said: “The rig remains in the original position and was reported to be carrying 280 metric tonnes of diesel oil on board in total split between a number of separate tank.
“During the inspection the salvors discovered that two of the fuel tanks appear to have been breached, however, it is unclear at this time how much oil from those tanks has been released to the environment.
“Weather conditions have made it impossible for the team to continue the assessment today.”