Where the production of milk for sale on the fresh milk market at 'controlled' prices is subject to nontransferable quotas the holders of quota who wish to maximise profits have a motive to maintain production above the quota level to insure against variations in demand for over-quota sales and yield. The concept of 'production of milk as insurance' is used to clarify the way in which such behaviour gives rise to social costs which could be avoided in a competitive market, by a permissive attitude to arbitrage, or where quotas can be traded.