Have you seen the price of teak oil????? Flipping Heck, it's cheaper to buy a new garden table!!
For indoor wood (we have an ancient oak beam, and an Iroko mantelpiece) I've always used olive or sunflower oil.
Is there any reason why I can't use cooking oil on my garden furniture instead of teak oil? It's a teak-like wood and I can leave it a week or so for the oil to soak in and dry.