White mineral oil is considered a petroleum distillate because it is a product of refining petroleum. Manufacturers must label thier product like this....
You have to shake it well to mix the oil with the other ingredients (probably a solvent of some sort that sinks to the bottom of the bottle as the oil floats on top)
I don't believe many products on the market for fretboard care contain much if not any real lemon oil as extracted from the lemon peel through a process called cold expression (essential oil) or steam distillation (turpene) ... Many folks are duped into believing that lemon oil is the primary ingredient in these products. All one has to do is contact the manufacturer and request the MSDS that identifies the ingredients.
Old English lemon oil which is used for furniture polish and cleaner has very little lemon oil...enough to fragrance it...it is 90-100% white mineral oil. Generally most products for fretboard care are formuated to clean (using a distillate other than mineral oil or a solvent) and replenish the natural oils of wood that dry out over time (mineral oil) Some manufactuers have other proprietery formulas....but the most i've seen don't contain much lemon oil in the forumula.
It smells like lemon because lemon fragrence (usually lemon essential oil) is used as an additive and coloring is added as well to attain a yellow appearance for some products.
Cold pressed lemon oil is exspensive and wouldn't be cost effective for manufacturers to use as the primary ingredient. Cold pressed lemon oil is considered an essential oil. There is another process of steam distillation....it turns the oil into a turpene or mild solvent...this is even more expensive to produce.
I have heard stories of folks using steal wool, credit cards, razor blades, etc....I have researched many methods and used many formulas, and the best approach that i discovered, without the threat of harming the fretboard in any way, is to use a nylon bristled brush...essentually a tooth brush....the bristles get down into the crevices of the wood grain to lift the grime (mainly on rosewood)...without scraping or harming the wood.
Ebony is a bit more dense and doesn't require a lot of work to get clean because the wood doesn't have the deep grain as rosewood.
Even though companys label it as lemon oil with hardly any lemon oil, they are probably able to label it that way because they put a small bit of essential oil...enough to fragrence the product and can call it lemon oil.
EDIT:
D'Adrea states that they have real lemon oil in their product.
http://www.mveducation.com/invt/34737/