These are widely used for ratings upto 72.5kVA.
The dielectric oil acts both as an insulating medium and as an arc extinction medium. The contact separation takes place in steel tanks filled with oil. The gases formed due to the heat of the arc, expand and set the turbulent flow of the oil.
To assist the arc extinction process, arc control devices are fitted to the contact assembly. Theses are the same enclosed chambers of dielectric materials. The performance of oil circuit breakers depends on the effectiveness of these arc control devices.[This is a 2 minute concept sketch drawn especially for exam point of view.