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* U.S. crude stocks fell by 1.8 million barrels -API
* Positions harden in Ukraine crisis
* New protest shuts Libya's Zultun, Raquba oilfields
* U.S. dollar falls
* Coming up: EIA inventory report due 10:30 a.m. EDT (1530 GMT) (Adds API data, market reaction)
By Elizabeth Dilts
NEW YORK, May 6 U.S. crude futures settled nearly unchanged on Tuesday, but later rose in post-settlement trade after industry group the American Petroleum Institute reported that crude stocks decreased last week, defying analysts' expectations for a build.
U.S. commercial crude inventories fell by 1.8 million barrels last week, with stockpiles at the Cushing, Oklahoma, delivery hub falling by 1.5 million barrels, the API found.
Analysts polled by Reuters had estimated a 1.4 million-barrel build, putting crude stocks at a record high for the third week in a row.
The U.S. Energy Information Administration (EIA) will issue its official inventory report on Wednesday.
Brent prices fell on Tuesday, pressured by resuming Libyan supply.
U.S. crude settled 2 cents higher at $99.50 a barrel, which analysts attributed to traders taking profits as they await the EIA's official inventory data. U.S. crude prices climbed 42 cents in post-settlement trade and were last at $99.90 by 5:02 p.m. EDT.
Brent crude fell 66 cents to 107.06 per barrel.
Analysts noted U.S. crude oil prices have traded in a range between the 200-day moving average of $100.57 per barrel and 100-day moving average of $99.35.
"We caught support on the 100-day and hit a wall on the 200-day," said Oliver Sloup, director of managed futures at iitrader.com. "There was some profit-taking ahead of the inventory report."
Last week, EIA data caused a sell-off of nearly 2 percent from U.S. oil futures over two days after its report showed U.S. crude stocks hit a record high in the week to April 25, led by another steep increase on the Gulf Coast.
Positive economic data also supported U.S. crude Tuesday as the U.S. trade deficit narrowed in March on rebounding exports.
The U.S. dollar fell to an eight-week low against the euro, another bullish factor for U.S. oil and other commodities priced in the dollar as a weak greenback makes them cheaper for traders.
Ukraine on Tuesday was quieter than in recent days, but this week is the deadliest since the separatist uprising began, which has helped put a floor under oil prices, traders said.
"The market is balancing a weak fundamental picture against the worry that we could see a disruption in Russian supplies," said Gene McGillian, analyst at Tradition Energy in Stamford, Connecticut.
Libyan exports have pressured Brent oil prices in recent weeks even though the vital southern El Sharara oilfield remains closed and new protests have shut the Zultun and Raquba oilfields.
Oil output in Libya now totals 250,000 barrels per day, compared with 1.4 million bpd in mid-2013. Government officials said they hope to reopen key oilfields within a week.
(Additional reporting by Edward McAllister in New York, Peg Mackey in London and Jacob Gronholt-Pedersen in Singapore; Editing by Susan Thomas, Keiron Henderson, Peter Galloway, Meredith Mazzilli and Steve Orlofsky)