(wikipedia)

WD-40's main ingredients, according to U.S. Material Safety Data Sheet information, are:

* 50%: Stoddard solvent (i.e., mineral spirits -- primarily hexane, somewhat similar to kerosene)
* 25%: Liquified petroleum gas (presumably as a propellant; carbon dioxide is now used instead to reduce WD-40's considerable flammability)
* 15+%: Mineral oil (light lubricating oil)
* 10-%: Inert ingredients
The German version of the mandatory EU safety sheet lists the following safety relevant ingredients:

* 60-80%: Heavy Naphtha (petroleum product), hydrogen treated
* 1-5%: Carbon dioxide