Combustion is a form of oxidation in which a fuel combines rapidly with oxygen releasing a substantial amount of heat.

The basic combustion reaction for a fuel oil is:

The above reaction indicates that 2.67 lbs. of oxygen are required to react with one lb. of carbon. Because air is 23.2% oxygen it required 11.5 lbs. of dry air to react with one Ib. of carbon. For every pound of carbon burned, 3.67 lbs. of carbon dioxide are produced.

In burning fuel oil, oxygen is also required to react with hydrogen and sulfur.

The overall reaction is:

C_XHyS_z+ 32/12 0₂ + 8y0₂ = 44/12 C0₂ + 9yH₂0 + 2z S0₂.