In the oil industry, the major product transported by sea has previously been crude oil. However, more and more refined products are also being transported by sea. Oil tankers deliver around 2.5 billion cubic meters of crude oil and refined products each year, and provide the next most efficient transport system after oil pipelines. Tanker sizes range from inland or coastal tankers that hold a few thousand cubic meters, up to ‘Ultra Large Crude Carriers’ (ULCC) that can hold up to 650,000 cubic meters. Tankers have different compartments and are often equipped with a marine tank monitoring and alarming system, such as the KROHNE CARGOMASTER, which uses radar-based level measurement sensors. Most tankers also have inert gas blanketing systems, using mainly nitrogen, that avoid the possibility of any explosive gas mixtures being present in the ullage space above the product.