This covers all residual (heavy) fuel oils (including those obtained by blending). Kinematic viscosity is above 10 cSt at 80 degrees C. The flash point is always above 50 degrees C and density is always more than 0.90 kg/l.
Low sulfur content: heavy fuel oil with a sulfur content of less than 1%
High sulfur content: heavy fuel oil with a sulfur content of 1% or more.