* Saudi Arabia acting to lower prices - Gulf source * U.S. crude inventories rose last week - Poll * Coming up: API oil data 4:30 p.m. EDT Tuesday (Recasts, updates prices, market activity; changes byline and dateline, pvs LONDON) By Robert Gibbons NEW YORK, Sept 18 (Reuters) - Oil prices slipped on Tuesday, extending the previous session's slide, as investor focus shifts from the likely economic benefit of central bank stimulus to concerns about sputtering global economic growth that prompted the U.S. Federal Reserve to launch its bond-buying program. Also pressuring oil, a senior Gulf source said Saudi Arabia is working to lower oil prices and is producing around 10 million barrels per day and that a majority of OPEC members want oil prices around $100 per barrel and would be increasing production over the next few months. "Unless there is a major supply disruption in the Middle East, there is nothing to push it higher," said analyst Andrey Kryuchenkov at VTB Capital. "Saudi will seek to drive it closer to $100 and everyone knows it." Brent prices rose seven straight sessions before settling 2.4 percent lower on Monday, benefiting first from growing expectations that the Fed would act to bolster the economy, and subsequently from the actual launch of the stimulus program on Thursday after a two-day policy meeting. Brent November crude fell 40 cents to $113.39 a barrel by 11:39 a.m. EDT (1539 GMT), having dropped as low as $112.59. U.S. October crude was down 32 cents at $96.30 a barrel, having swung from $95.39 to $97.23, straddling the 200-day moving average of $96.57. The October contract expires on Thursday. Monday's steep, rapid intraday sell-off left Brent down more than $5 at the day's low and U.S. crude off more than $4. The sell-off came after Brent and U.S. crude did not extend the previous week's surge on the Fed stimulus that sent prices to four-month highs. Traders explained the plunge variously as stemming from computer-based trading, sell stops triggered in a session characterized by light trading volume on the Rosh Hashanah holiday and from heightened expectations that the U.S. and its allied consumer nations would release oil reserves. The possibility that one or more market participants sold oil futures to generate cash after being hit by margin calls from losses in another market also was floated. "The dramatic sell-off does not appear to have been driven by anything fundamental in the market. It looks as though it was triggered by computer trading system-type selling," said Tony Machacek, an oil futures broker at Jefferies Bache. "We've seen a steady increase in prices, so maybe the market was a bit overbought and susceptible to a long-liquidation move to the downside." The U.S. Commodity Futures Trading Commission said it was looking into the drop in prices and checking with exchange operators CME Group and Intercontinental Exchange . A stronger dollar on Tuesday also weighed on oil prices, as the euro fell against the U.S. currency as uncertainty about whether or not debt-stressed Spain will request a bailout. A strengthened U.S. currency can put pressure on dollar-denominated commodities such as oil. (Additional reporting by Alex Lawler in London and Luke Pachymuthu in Singapore;Editing by Sofina Mirza-Reid)

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