Oil and gas exploration and development is extending into deeper water in the Gulf of Mexico. The current record is 3,051 m (10,011 ft) in Chevron's Toledo prospect in the Alaminos Canyon Block 951 in the Gulf of Mexico. This report was prepared to support the Minerals Management Service (MMS) regulatory decisions for oil and gas leasing. Given the recent development of subsea technologies, it is not surprising that very little information is readily available on the potential environmental effects. This report represents the compilation and synthesis of existing published and unpublished literature on the environmental effects of subsea operations on the deepwater environment. Technical experts from the oil and gas industry, regulatory agencies, and academic institutions were also consulted to identify potential environmental issues.