High-sulfur fuel oil (HSFO), The alternative to using marine fuels with such low sulfur content in ECAs is the use of scrubbers. RMK 500 & 700 fuels are made from the same basic components as lower viscosity fuels, with cutters (such as cycle oils, gas oil, etc) being used in varying. High Sulphur Fuel Oils are the most widely used marine fuels outside the Sulfur Emission Control Areas (SECA) zone, but from. While high sulphur fuel oil (HSFO) can be converted to low sulphur. It is used to generate motion and/or heat that have a particularly high viscosity. Heavy fuel oils continue to be used in the boiler "lighting up" facility in many coal- fired power plants.