Oil fell back on Thursday, from above $120 a barrel, after the International Energy Agency pledged to help out with additional supply if Tropical Storm Gustav damages US oil installations in the Gulf of Mexico. The storm is forecast to reach hurricane status as it approaches the Gulf of Mexico, home to a quarter of US crude oil production and 15 percent of its natural gas output. US crude oil for October delivery was down 15 cents at $118.00 a barrel by 1503 GMT. It reached an intraday high of $120.50 a barrel. London Brent crude was up 3 cents at $116.25 a barrel. The International Energy Agency has said it is ready to release strategic oil stocks if needed. The agency, adviser on energy issues to 27 industrialized countries, released oil product stocks in 2005 after Hurricane Katrina. “The impact of Gustav could now be assuaged by this intervention,” said Christopher Bellew, of Bache Commodities Limited.