Lawn mower (Petrol) (Dursley GL11)

This lawn mower never got much use and was always reliable before being placed in storage. However it has not been used for 15-20 years and has no fuel in it at the moment so I haven't been able to try it out. It has been stored under a tarpaulin and in a relatively dry place (between a wall and laurel hedge) since it was last used, but it now has a lot of surface rust. The engine appears to turn when I pull the cord but no idea if it will work when fuelled ! May need oiling.