As your bicycle chain turns around the gear sprockets and pedal cranks, it creates friction. In order to limit the amount of wear on the chain and sprockets caused by this friction, you need to regularly lubricate your chain. Many riders use some type of a light oil to lubricate their chains. This is appropriate in many cases, but you should consider your normal riding conditions to find the best lubricant for your biking needs.
A light oil is typically best for your bicycle chain in average to dry riding conditions. Light oils are good at penetrating the bushings of chains to minimize the amount of wear that occurs between the links. You apply this type of oil by turning the pedal crank backwards and squeezing out a line of oil down the chain rollers. Phil Wood Tenacious Oil and Tri-Flow are popular light oils among cyclists.
If you typically ride in very rainy or wet conditions, a thick oil or grease like that used on motorcycle chains is more appropriate to your purposes. Bicycle mechanic Sheldon Brown recommends using this type of oil after you mix it with a volatile solvent to thin it. The mixture will better penetrate chain bearings, and the solvent will evaporate to leave the thick chain grease. The main problem with thick lubricants, however, is that they pick up more dirt as you ride, which can grind your gears down over time if you do not regularly change the oil.
Wax is the best lubricant choice if you live in extremely dry conditions, according to cycling expert and author Jim Langley. Though it is more of a challenge to apply, melted wax very effectively penetrates the chain and then dries in place. Dirt and road grime do not stick to the wax as you ride, and as long as the conditions remain dry the wax can last on the chain for months. The wax naturally flakes off over time, meaning that you do not need to degrease the chain like you would with other oils.
Though spray lubricants are easy to apply to a chain and can penetrate well, they are not a good choice in any riding condition. According to BicycleTutor.com, spray lubricants like WD-40 are too thin to have an effect on fast-moving parts like a bicycle chain. Additionally, the solvents in these types of lubricants act as degreasers, stripping away any lubricant placed on the chain by the manufacturer and effectively increasing the amount of wear on your chain.