Medium Oil Bowling Balls. We have sorted all the bowling balls available by oil volume so you can find with ease the ball you need. Medium Oil balls are usually the standard (average hooking) balls available and meant to be used on the medium oil patterns. Medium Oil balls are great on Typical House Shot's (THS) and for when the heavier oiled lane conditions start breaking down. A medium oil ball will be a great choice for anyone who bowls as they will not be to strong or to weak on most oil conditions.