Oils come in a few categories, including petroleum based, synthetic based, or bio oils. Some valve oils are blends containing two or three of these types of oils, and others are purely one kind only.
Purely petroleum valve oils tend to have a strong odor due to the uncontrolled light fractions common in kerosene (jet fuel) or lamp oils. These odors indicate that the oil is evaporating quickly, and the odors can be irritating to your throat or lungs (not so good for wind players!) The main drawback of petroleum valve oils is that they don't last very long on the pistons or rotors of brass musical instruments. When they evaporate, they tend to leave stains behind, and these stains are difficult to remove.
Synthetic oils are distilled from petroleum, natural gas, or bio fuels. The hydrocarbons are separated into their different weights, making an oil with incredible purity and quality control at the molecular level. The light fractions that would have odors are completely removed, and the remaining oil is very slow to evaporate. A synthetic oil on your horn has similar properties to synthetic oils in a motor -- long lasting, low odor, and very resistant to oxidation. They also have a wonderful, silky-smooth feel that players love.
Bio oils are either made like synthetic oils -- distilled to separate various fractions of oils and blended to make the right weight -- or are pure vegetable or plant essential oils. Some essential oils have excellent resistance to oxidation, and we definitely take advantage of this property in our valve oils.
At Ultra-Pure Oils, we use only the highest purity synthetic and bio oils, and we blend the oils to meet the exact requirements of trumpet, french horn, cornet, or other musical instrument.
Finally, a note about switching valve oils. If you were using a petroleum valve oil for some time, your instrument will probably have residues and stains from the oils. Since synthetic oils don't evaporate so quickly, they tend to loosen up old stains and grime from inside your horn, and this grime can make your valves stick. It's not so much a chemical reaction between types of oils, but more of the cleaning power of synthetic oils that is loosening up old grime and making your valves stick. Keep cleaning the horn or send it to a repair shop for deep cleaning and you will make a successful change over to synthetic valve oil. It is definitely worth the effort.