Best wood preservative?

[wjwren]

Buying a small shed which will be hidden from view, what is the best protection for the wood. Im after something to put on and leave, not fussed if it looks a dodgy colour. Any views on using old engine oil and diesel?

[wjwren]

V40TC said:

Sikkens is what I would use
spendy but worth it .

I love Sikkens, but not cheap. But good product.