I think it was Nathional Geographic about a month or two ago talked about the very same thing.
All oil started out as plant life.Eons of years and pressure determined weather it would end up as natural gas,crude oil ,peat or coal. It doesn't make much diff if it's wood chips or dandilions the BTU's are there if you figure how to extract them in a usable form .
Some years ago on the discovery channel this guy in Pa was making his own home brew gasoline.He used an old fuel oil tank as an oven and filled it full of wood,garbage,anything organic and cooked it on a wood fire under pressure.Bingo,crude oil.He ran this stuff through a simple vacuum still,crude gasoline.Most likely about 70-80 octane but it worked .
Oh,for what it's worth,there are several gallons of crude oil in an old tire.The basic rational behind modern science,Matter is neither made nor destroyed,it's form is changed.The tire started out as oil and to oil it shall return .