Must be a couple of months since this one last came up - my cut-and-paste standard response ...
Oils that cure
Some oils cure, that is they will set in the wood, and some do not. If you use one that does not cure there is a chance it might go rancid in the wood. With an object as small as a spoon there is only a small chance - I have only seen it with larger things such as salad bowls which have been regularly oiled with olive oil and rarely washed. More of a problem is that the oil will wash out of the wood when you wash the spoon, so it will need re-oiling periodically if you want your spoon to remain protected. That is why we use and recommend oils that cure.
DIY oils
Oil is naturally quite viscous, so many oils sold for DIY use contain chemical thinners which help them penetrate the wood. The thinners are not food safe, but because the oils are not sold for food use there is no obligation for manufacturers to even state their presence on the label, let alone say they are poisonous. Whilst the amount of thinners that would go into your body through eating with a spoon coated in such an oil is minimal, it is not what I would choose to put in my mouth!
Recommended oils
For small quantities for personal use we would recommend some type of cooking oil. Walnut oil is the best; it cures quite quickly and smells lovely, but obviously is not good for nut allergy sufferers. Linseed oil sold for food use is also excellent and safe for those with allergies, health food shops sell it, often calling it flaxseed oil. Sunflower oil also cures, but it will take much longer. Olive oil does not cure, so is not recommended. We use large quantities as Robin oils bowls too, so bulk buy cold pressed linseed oil from an agricultural merchant; it is sold for feeding to horses as it makes their coats shiny!
more discussion on this thread
Nicola