California Code, Public Resources Code - PRC § 3329

The unit operator shall be authorized on behalf of and for the account of all the respective owners or possessors of the mineral rights within the unit area to supervise, manage and conduct the further development and operations for the production of oil, gas and other hydrocarbon substances from the unit area pursuant to the powers conferred, and subject to the limitations imposed by the provisions of this article and by the order of unitization.

The obligation or liability of the lessee or other owners of the mineral rights in the several separately owned tracts for the payment of unit expense shall at all times be several and not joint or collective and in no event shall a lessee or other owner of the mineral rights in the separately owned tract be chargeable with, be obligated or liable, directly or indirectly, for more than the amount apportioned, assessed or otherwise charged to his interest in such separately owned tract pursuant to the order of unitization and then only to the extent of the lien provided for in this section.

Subject to the provisions in the order of unitization, the unit operator shall have a lien upon all drilling and production equipment in and to each separately owned tract, and upon the portion of the unit production allocated to the working interest therein, to secure the payment of the amount of the unit expense chargeable to and assessed against such separately owned tract.  Such lien may be enforced by the unit operator, as the agent of the respective owners or possessors of the mineral rights within the unit area, as against noncarried working interest owners, in the manner set forth in Section 3330.  The interest of the lessee or other person who by lease, contract or otherwise is obligated or responsible for the costs and expenses of developing and operating a separately owned tract for the production of oil, gas and other hydrocarbon substances in the absence of unitization shall be solely responsible for and chargeable with any assessment for unit expense made against such tract.