UPDATE 4-Oil operations in Gulf unaffected by storm

* Hermine expected to make landfall within 24 hours

* No U.S. production cuts reported

* Mexico's Pemex says no damage seen Monday

* Valero Corpus Christi preps for rough weather (Updates first paragraph, adds Shell saying there is no impact)

HOUSTON, Sept 6 (Reuters) - BP Plc (BP.L)(BP.N), the largest oil producer in U.S.-regulated areas of the Gulf of Mexico, and Shell Oil Co (RDSa.L) said Monday that Tropical Storm Hermine was not affecting their offshore operations.

Hermine, which formed early Monday morning, was churning toward landfall by late Monday near the Mexico-Texas border.

Hermine was forecast to take a path between both U.S. and Mexican major offhsore oil and natural gas production areas.

For the United States, the Gulf of Mexico's offshore oil patch provides 30 percent of national crude output and 11 percent of the country's natural gas production.

Oil companies were carefully monitoring Hermine on Monday.

"It's not impacting any of our operations," said BP spokesman Neil Chapman.

Shell said operations and staffing at its offshore facilities were unaffected by the storm.

Valero Energy Corp (VLO.N) said production at its 315,000-barrel-per-day (bpd) Corpus Christi, Texas, refinery was at planned levels, but the plant was preparing for possible rough weather from Hermine.

Flint Hills Resources and Citgo Petroleum Corp also operate refineries in Corpus Christi, which the U.S. National Hurricane Center said faces a 70 percent chance of tropical storm force winds from Hermine.

No cutbacks in oil and natural gas production had been announced by U.S. companies as of 13:30 p.m. CDT (1830 GMT).

Pemex, Mexico's state-run oil company, said there were no reports of damage to its facilities in or near the Gulf of Mexico due to Hermine.

Hermine is also expected to pass south of three refineries in Corpus Christi.

The U.S. National Hurricane Center has said Hermine could approach hurricane strength by the time it makes landfall. (Reporting by Erwin Seba; editing by Jeffrey Benkoe and Kenneth Barry)