The storage tanks at an oil terminal may includes fixed roof tanks, internal floating roof tanks and external floating roof tanks. Floating roof tanks are generally used for more volatile products to reduce evaporation loss. Fixed roof tanks which have a vapor space above the product and which breathes in or out as the product is removed or the tank is filled. Some tank may be fitted with internal heating coils using hot water or steam to keep the contents warm. This reduces the viscosity of the product to ease transfer and pumping. Terminals may also have ‘Horton spheres’ which are used to store liquefied petroleum gases such as propane and butane (see left foreground of the above Kowloon oil depot).