Fuel oil is a type of liquid petroleum product that is used primarily as a source of energy for heating and powering engines. It is derived from crude oil through a refining process. There are several grades of fuel oil, but they are generally categorized into two main types:

1. Distillate Fuels: These are lighter and cleaner-burning fuels, such as:

   • Diesel Fuel: Used in diesel engines and for heating.
   • Kerosene: Often used in jet engines, heating systems, and as a solvent.

2. Residual Fuels: These are heavier and more viscous, used primarily in large industrial applications:

   • Bunker Fuel: Commonly used in marine engines and large industrial burners.
   • Heavy Fuel Oil (HFO): Used in power plants and large ships.

Fuel oils are used in various applications, from residential heating to powering ships and industrial machinery. They can be stored in tanks and are typically pumped to burners or engines. Due to environmental regulations, there is a growing shift towards cleaner energy alternatives and improvements in fuel oil technology to reduce emissions and environmental impact.