43 CFR 3106.72: Continuing obligation of an assignor or transferor.

(a) The lessee or sublessee remains responsible for performing all obligations under the lease until the date the BLM approves an assignment of record title interest or transfer of operating rights.

(b) After the BLM approves the assignment or transfer, the assignor or transferor will continue to be responsible for lease obligations that accrued before the approval date, whether or not such obligations were identified at the time of the assignment or transfer. This includes paying compensatory royalties for drainage. It also includes responsibility for plugging wells drilled and removing facilities installed or used before the effective date of the assignment or transfer.