Okla. Stat. tit. 17, § 511

The obligation or liability of the lessee or other owners of rights in the several separately owned tracts for payment of unit expense shall at all times be several and not joint. At no time shall a lessee or other owner of rights in a separately owned tract be chargeable with, directly or indirectly, more than the amount apportioned to its interest in such separately owned tract pursuant to the plan of unitization. Subject to such reasonable limitations as may be set out in the plan of unitization, the operator shall have a first and prior lien upon the leasehold estate in and to each separately owned tract and the interest of the owners therein in and to the unit production and equipment in possession of the unit, to secure the payment of unit expense charged to such separately owned tract.