UKCS United Kingdom Continental Shelf. ULCC Ultra Large Crude Carrier - tanker of over 300000 tonnes. Unaccounted for (crude oil) Represents the arithmetic difference between the calculated supply and the calculated disposition of crude oil. The calculated supply is the sum of crude oil production plus imports minus changes in crude oil stocks. The calculated disposition of crude oil is the sum of crude oil input to refineries, crude oil exports, crude oil burned as fuel, and crude oil losses. Upstream Upstream covers the exploration, production and transport prior to refining.