Animal and Vegetable oils: Animal oils and fats used to be used for greasing horse and cart axles, but animal fats are not suitable for motorcycle engines as they oxidise (burn) at low temperatures and will form a clogging gum or varnish.
Most vegetable oils have the same drawbacks as animal fats, except castor oil.
Castor oil has very good lubrication properties when under heavy load. Unfortunately, castor oil still oxidises very easily, which often means motorcycle engines running on castor oil need frequent engine strips to remove deposits. Castor oil was widely used in racing applications many years ago, and is still sometimes used today.
Mineral oils: Mineral oils are made by the fractional distillation of crude oil, which is the same method used to extract petrol from crude oil.
Mineral oils are able to withstand higher temperatures and are much less prone to oxidation which makes them much more suited to conditions inside an engine.
Semi-Synthetic oils: Semi-synthetic oils are used in motorcycle engines as a good compromise between performance and expense as many motorcycle engines don’t require a fully synthetic oil to operate. A semi synthetic oil is an oil that is supplemented with additives which prolong the oil service life and reduce the wear to acceptable level.
Fully synthetic oils: Synthetic oils are chemically manufactured (so a good full synth oil should be 100% man made and not contain any oil out of the ground).
Although they are generally more expensive, synthetic motorcycle oils don’t suffer from oxidation and have extremely high lubrication qualities which makes them ideal for high power, high speed engines.