Oil Spill Risks from Tanker Vessel Lightering: A Marine Board Report
Authors: Ward E.G. , Clark T. 
Published: October 2008

Abstract
The Marine Board has recently completed a study associated with lightering which concludes lightering operations in U.S. waters have an excellent safey record [1]. Tanker-based FPSO's have been used as deepwater production systems in other areas of the world, and are now being considered for the Gulf of Mexico. Offloading operations from FPSO's in the Gulf of Mexico should be at last as safe as lightering since many of the operations for lightering and offloading are similar.

Introduction
Tanker-based FPSO's are being studied for use as a deepwater production system in the Gulf of Mexico [2]. While FPSO's have been used in other offshore areas around the world with good success, concerns have been raised regarding potential risks associated with their use in the Gulf of Mexico [3]. The Marine Board has recently completed a study of risks associated with lightering operations in the U.S offshore. That study showed most lightering in the U.S. occurs in the Gulf of Mexico, and lightering operations in U.S. waters have an excellent safety record. These results for lightring are also pertinent to the assessment of risks which might be associated with tanker-based FPSO's operating in U.S. water, as many of the operations for lightering and offloading are similar.

Marine Board Study of Lightering.
The Coast Guard Authorization Act of 1996 required the U.S. Coast Guard (USCG) to coordinate with the Marine Board of the National Research Council (NRC) and study the risks of oil spills from lightering in U.S. waters.Investigate the frequency and risks of accidents from lightering operations,Assess the existing regulatory and management frameworks responsible for lightering,Recommend measures that could reduce the risks of oil spills.
Accordingly, the Marine Board assembled a study committee whose members have expertise, experience, and contacts in tanker and lightering operations, risk assessment, regulatory and management practices, accident prevention, and environmental protection. Table 1 shows the committee members, their affiliations, and areas of expertise.
The committee reviewed lightering operations, current management and safety standards, risks, and data on lightering operations and incidents. Their investigations included studies of existing databases and reports; meetings and workshops with representatives from industry, regulatory agencies, and environmental groups; and correspondence with shipping and lightering companies and with industry organizatons. Their final report was reviewed in accordance with NRCs peer review and Marine Board review processes.
The following sections are summarized from their report [1].

Lightering in U.S. Waters.
Lightering is simply the ship-to-ship transfer of cargo. With the United States' growing demand for imported oil, more and more of that oil is shipped from the Mid-East or Africa in large tankers. These large tankers, called VLCC's and ULCC's (very large and ultralarge crude carriers), are a very economic way to transport the large amounts of oil to the U.S. [1,4]. However these VLCC's and ULCC's are much too large to transit the ports where the oil is needed by the various refineries. Thus the evolution of lightering. A smaller tanker (service ship), capable of transiting the waterways to the discharge berth, will come alongside the VLCC or ULCC at sea, receive a portion of the oil and then take that parcel of oil into port (this is typically known as a lift).