The California Oil Spill Prevention Act of 1990 established statutory Petroleum Tank Ship Escort requirements for regulations governing vessel movements in California ports and harbors.

Among the resultant regulations is a requirement that "...all tank vessels carrying 5,000 or more long tons of oil as cargo..." employ a tugboat escort from the approaches to San Francisco Bay to any of, or between, the ports or anchorages within the bay. The regulations determine the minimum pulling capability of the escort tug or tugs based on applicable parameters:

  1. Displacement tonnage of the tank ship or deadweight tonnage of the tank barge.

  2. Dynamic pulling capability of the tug or tugs, expressed in KIPS (an engineering unit of force).

  3. Maximum current at any point traversed during the vessel's transit of the bay.

  4. Whether the tank vessel is a barge or a self-propelled ship.

  5. The geographical zone.

A tank ship carrying such cargo through the bay must calculate the required California State-mandated KIPS and obtain sufficient towage to meet the escort requirement. Since arriving vessels are frequently unfamiliar with this requirement, the Marine Exchange of the Bay Area, as secretariat for the State of California, monitors the KIPS required by the ship. As a practical matter, the ship's agent, in cooperation with the Marine Exchange and the tug supplier, advises the ship of the required KIPS to be ordered by the agent or owner's representative. For tank barges, escort tugs are matched on a one-to-one correlation between deadweight tonnage and the escort tug's braking force (KIPS).

The State of California divides San Francisco Bay into several geographic zones for purposes of the Escort Regulations, and tug escort charges are calculated with reference to these zones:

Zone 1: Point Bonita entrance light to the Golden Gate Bridge
Zone 2: Golden Gate Bridge south to Point San Bruno and north to Point San Pablo (essentially the greater Bay Area; includes the Chevron Long Wharf, Anchorages #7 and #9)
Zone 3: All waters from the southern end of Zone 2 to one mile north of the San Mateo Bridge
Zone 4: The navigation channel from one mile north to one mile south of the San Mateo Bridge
Zone 5: From the eastern boundary of Zone 2 to the western approaches to the Carquinez Bridge at Light 15
Zone 6: All waters from Light 15 through the Carquinez Strait into the Sacramento Ship Channel and east on the San Joaquin River (includes terminals at Pacific Refining, Oleum, Wickland, Crockett, Benicia, Exxon, Shell Martinez, Amorco, Wickland Martinez, Avon, and PG&E Pittsburg, Dow Chemical)

Subject tank vessels are required to have tug escorts in Zones 1, 2, 4, and 6.

Main fixes: added the missing connector before "The Marine Exchange" (was a run-on), hyphenated "self-propelled" and "one-to-one," standardized "KIPS" capitalization throughout, straightened quote marks, and made zone formatting consistent (colons instead of mixed punctuation). One thing to check: your Zone 6 terminal list ends "...PG&E Pittsburg, Dow Chemical" — looks like a missing "and" or comma between those two, worth confirming they're separate entries.