FACTBOX - Gustav cuts U.S. oil, gas, threatens commods

(Reuters) - Forecasters say Hurricane Gustav could be the first major threat to the U.S. Gulf of Mexico oil fields and ports since hurricanes Katrina and Rita in 2005.

The Gulf is the source of 25 percent of domestic oil and 15 percent of the natural gas. More than a third of U.S. refining capacity is on the U.S. Gulf Coast.

In the "cone of uncertainty" is New Orleans, a big port handling raw material and foodstuff. The Port of South Louisiana is the largest U.S. port in tonnes handled.

On the western edge of the "cone" is Houston, a major port, oil refining and crude oil and natural gas hub.

Katrina and Rita were Category 5 storms, the top of the hurricane intensity scale. Katrina hit New Orleans in August 2005. Rita hit near the Texas-Louisiana line that September.

Gustav, expected to come ashore by Tuesday on the Gulf Coast as a Category 3, a major hurricane. But it strengthened to near Cat 5, as it approached Cuba on Saturday.

---- IMPACTS OF GUSTAV ----

- The U.S. Minerals Management Service said Saturday 998,000 of 1.3 million barrels per day (bpd) of oil production (76.8 percent) and 2.75 billion of 7.4 billion cubic feet per day of gas (Bcfd) production (37.2 percent) had been shut in anticipation of Gustav. Up from 6.62 percent of oil and 1.84 percent of gas Friday.

- MMS said personnel evacuated from 223 of 717 manned production platforms (31.1 percent) and 45 of 121 drilling rigs (37.2 percent) currently operating in the Gulf.

- NYMEX crude oil shot up $3 before settling down 13 cents at $115.46 a barrel Friday. stopped taking gas from producers Saturday on systems with 6.72 Bcfd of capacity.

- El Paso Corp said its Tennessee and Southern Natural gas pipeline systems saw throughput cuts totaling 637 mmcfd.

- Shell Oil Co, largest Gulf producer, said it was shutting down all 510,000 bpd oil equivalent and withdrawing 1,300 workers.

- Majors BP Plc and Chevron said they shut output in path of Gustav.

- Others including Exxon Mobil, Hess, Petrobras, Marathon, Anadarko cut output and evacuated.

---- REFINERY IMPACTS OF GUSTAV ----

- Murphy Oil Saturday said it was shutting its 120,000 bpd refinery near New Orleans, some production.

- Four Valero Energy Corp refineries, with a total capacity of about 920,000 bpd, reduced runs.

- ConocoPhillips said it was shutting refineries, near Lake Charles and New Orleans, capacity about 485,000 bpd.

- Motiva Friday cut staffing at its 220,000 bpd refinery in Norco, Louisiana, but kept operating normally.

- Marathon said shutting its 250,000 bpd Garyville, Louisiana, refinery.

---- SHIPPING IMPACTS OF GUSTAV ---

- River pilots said Mississippi River traffic at New Orleans halted inbound at noon (1700 GMT) Saturday, outbound as of 6 p.m. central U.S. time (2300 GMT).

- Calcasieu River pilots at Lake Charles said all traffic to halt at midnight (2400 GMT).

- Sabine Pass entry to Beaumont and Port Arthur, Texas, shut inbound as of 3:30 p.m. central U.S. time (2030 GMT) and to halt outbound Sunday afternoon.

- Preparations for possible tropical storm force winds were underway at ports of Houston; Gulfport-Biloxi and Pascagoula in Mississippi and Mobile in Alabama.

---- KATRINA AND RITA IN 2005 ----

- Katrina flooded 80 percent of New Orleans, killed 1,500 people along the Gulf coast and caused $80 billion in damage.

- There was near total shutdown of Gulf oil and gas output at that time, 1.5 million bpd of oil and 10 Bcfd of gas.

- Twenty-nine percent of U.S. refining was shut at peak.

- Winds and waves destroyed 124 platforms and damaged about 50 others, damaged or wrecked 535 pipeline segments and sank or set adrift 28 drilling rigs, MMS said.

- In Katrina, the Port of New Orleans suffered $1.6 billion in damage, the Port of South Louisiana $1,850,000 in damage, but they resumed at least partial operations within days.

---- IMPROVEMENTS AFTER KATRINA AND RITA ----

- Strengthened existing platforms and design standards for new ones, raised worst-case wave-height criteria from 70.5 feet

to as much as 91.9 feet.

- Tightened mooring, raised jackup heights for drill rigs.

(Reporting by Bruce Nichols, Chris Kelly and Marcy Nicholson; Editing by Xavier Briand)