Used engine oil is highly toxic and a small amount can contaminate water over a wide area.
Used oil can be reprocessed into various fuel oils.
It is illegal in many countries to dispose of engine oil by disposing of it in the environment.
Petrol should not be be disposed of in the environment. It is too easy for it to get into groundwater which would cause pollution over a wide area.
It is worth checking if a local facility exists to handle fuels such as oil, petrol and diesel in a proper manner.