The term 'Diesel Oil' is a type of fuel used in diesel engines. It is composed of hydrocarbons derived from petroleum and is often referred to as 'heavy fuel oil'. The acronym DERV stands for 'Diesel Exhaust Residual Vapour', which is the vapour produced when diesel oil is burned. This vapour is composed of a variety of pollutants, including carbon dioxide, nitrogen oxides, and particulate matter.