33 C.F.R. § 156.205
Lightering or Lightering operation means the transfer of a cargo of oil in bulk from one oil tanker less than 150 gross tons to another oil tanker less than 150 gross tons, or a cargo of hazardous material in bulk from one vessel to another, including all phases of the operation from the beginning of the mooring operation to the departure of the service vessel from the vessel to be lightered, except when that cargo is intended only for use as fuel or lubricant aboard the receiving vessel.
Marine environment means-
Service vessel means the vessel which receives a cargo of oil or a hazardous material from another vessel in a lightering operation.
Vessel to be lightered means the vessel which transports a cargo of oil or a hazardous material to a place within the marine environment for transfer of that cargo to another vessel for further transport to a port or place subject to the jurisdiction of the United States. The term "vessel to be lightered" does not include drilling rigs, or offshore supply vessels transferring cargo intended for use as fuel or lubricant aboard the receiving vessel.
Work includes any administrative duties associated with the vessel whether performed on board the vessel or onshore.
33 C.F.R. §156.205