In the UK, a Compulsory Stock Obligation (CSO) is a minimum stock of fuel reserves that must be held by a supplier against shortages or interruptions in supply. The scheme is administered by the Department of Trade and Industry (DTI).

Companies incur an obligation if they are a supplier of a volume of 100,000 tonnes per annum or greater. This obligation is assessed as being a holding of 67.5 days' stock (50 days for the UK).