Petroleum products are derived from crude oil and are very complex mixtures of organic chemicals which vary widely in molecular weight, physico-chemical properties, environmental fate, behaviour and toxicity. On the basis of annual production/consumption figures the most important products to man are (in this order); automotive gasoline (“petrol”), automotive diesel fuel, residual fuel oils (Nos 4, 5 and 6) and jet fuel (kerosine). Despite much lower production volumes, lubricating oils (particularly engine oils) are also very important. Of lower importance are fuel oils for domestic heating purposes (i.e. Nos 1 and 2). The increasing production volumes are broadly reflected in an increased risk of entry to aquatic ecosystems as indicated by use, storage and transport patterns.