After being taken from the ground crude oil is brought to the refinery where it is purified and separated for various uses. The major goal of most refineries is to produce as much gasoline as possible from the crude oil. Some of the processes employed are distillation, catalytic cracking, polymerization, alkylation, hydrogenation, isomerization and reforming. The products produced range from liquifled petroleum gas to waxes. One of the products is heavy fuel oil. This is the product with which we are primarily concerned.

Because of differences in equipment, types of operation and economics, different fuels are used in different plants. Basically there are four different grades of industrial fuel oil available:

No.2: This is a clear, relatively light oil. It is capable of being distilled or vaporized at normal temperatures and pressures.

No.4: A blend of No.5, No.6, and No.2. It can be unstable and tends to separate into its individual components.

No.5: This is a heavy, black, viscous residual oil.

No.6: Similar to but a heavier residual than No.5. It is the most common industrial fuel.

No.1 fuel oil is a domestic grade used almost exclusively for home heating.

No.3 fuel oil was obsolete and replaced by No.2