30 CFR § 556.710 - What is the effect of an assignment of a lease on an assignor's liability under the lease?
If you assign your record title interest, as an assignor you remain liable for all obligations, monetary and non-monetary, that accrued in connection with your lease during the period in which you owned the record title interest, up to the date BOEM approves your assignment. BOEM's approval of the assignment does not relieve you of these accrued obligations. Even after assignment, BOEM or BSEE may require you to bring the lease into compliance if your assignee or any subsequent assignee fails to perform any obligation under the lease, to the extent the obligation accrued before approval of your assignment. Until there is a BOEM-approved assignment of interest, you, as the assignor, remain liable for the performance of all lease obligations that accrued while you held record title interest, until all such obligations are fulfilled.