This paper reviews the legal and regulatory regime for decommissioning oil and gas platforms on the United Kingdom Continental Shelf (UKCS) and in the North Sea and the process followed by UK regulatory authorities in approving an exception (derogation) to the requirement to fully remove all structures. This exception allows the footings, i.e., the lower base section of the jacket structure, of large steel jacketed platforms to remain in-situ. The paper provides details on how UK Platform Ninian North (Ninian) was removed and the Comparative Assessment of decommissioning options prepared by the owners of the platform that supported the decision by UK regulatory authorities to allow the jacket footings to remain in-situ. The paper notes that the U.S. Outer Continental Shelf (OCS) Oil and Gas Regulations allow partial removal of platform jackets under some circumstances and that there are eight California oil and gas platforms which have jackets that would qualify for partial removal, i.e.,derogation, based on the criteria established for North Sea oil and gas installations.To obtain permit approvals from federal and state regulatory agencies to leave the lower portions of largeCalifornia platform jackets in-situ, the owners of the platforms will need to clearly demonstrate partially removing the jackets is the best overall (optimum) decommissioning option. This can be demonstratedby preparing Comparative Assessmentswhich evaluate platform decommissioning options using safety, technical, environmental, and economic (cost) criteria