i know the article Brian posted says that oak is a no no, but i have used field collected oak in numerous vivariums and have never had any problems. in fact, one piece has been used in several. just make sure you prepare it properly. i boil my pieces of wood for about an hour. if it's too big for a pot, i bake it, like Ed mentioned. and if it is too big for the oven, i bbq it. obviously, as Ed said, you must keep a careful eye on the wood when baking or bbq'ing.