The government required that all oil refineries in this country had to keep 90 days' supply of crude oil in Great Britain. To meet that requirement, a number of oil companies stored crude oil in the salt cavities at Plumley. However, they had to enter into an exchange deal with Shell, as the only refinery that could easily use the crude oil was Shell Stanlow. There were also problems with operations at Plumley in the build-up of sludge from the crude oil in the cavities. It was found that sludge was building up at a rate that increased with the movement in and out of the cavities. Therefore, the cavities hired by Shell and the most frequently used for the Stanlow refinery had the largest accumulation of sludge.
