LONDON, May 17 (Reuters) - Gasoline barge prices fell in northwest Europe on Thursday as motorists and businesses continued to curb their driving due to high euro-denominated prices and supplies started to build. Traders said stronger gasoline margins in April had encouraged refineries to pump more of the motor fuel which is now weighing on the flat price. "Margins and runs have been good recently, it's a bit of a correction," said one gasoline trader. Another said emerging market demand had dropped off slightly for the moment. The Mediterranean market is also a little weaker as refineries come back from seasonal maintenance. "Demand is not as strong as it was supposed to be, especially from the U.S.," said one gasoline trader. He added it was difficult to see any support in the near term, but strength could return when the U.S. hurricane season gets under way. On the naphtha side, the arbitrage to Asia is technically open, as the East/West differential is quite wide at $13.25 a tonne, but demand for naphtha cargoes in the Far East is subdued at present. Asia's top naphtha buyer Formosa Petrochemical is delaying naphtha shipments as it reduces operating rates at its 2.93 million tonnes a year cracking complex. It has also replaced a portion of its naphtha feedstock with gas. GASOLINE * No barges of benchmark Eurobob traded in the window, but some 6,600 tonnes traded ahead of the window at $998-$999 a tonne fob ARA. This is in line with Wednesday's trades in the window at $997-$999 a tonne. * The early trades came at premiums to the June swaps of $14.50-$15 a tonne. * Total and Chevron were on the sell side while buyers included Shell, Gunvor and BP. * Three trades came after the window at $991-$994 a tonne fob ARA. Total and Trafigura sold 2,000 tonnes apiece to BP, and Total sold another 2,000 tonnes to Gunvor. * Eurobob's crack to dated Brent BFO- was up at around $9.75 a barrel, from around $7.70 a barrel on Wednesday as product prices held up better than crude. * Four barges of premium unleaded gasoline traded in the window at between $1,008-$1,010 a tonne, in the middle of Wednesday's $1,005-$1,016 a tonne range. * Gunvor and Northville were sellers while Vitol and Glencore were on the buy side. * ICE Brent crude futures were down $1.52 to $108.23 a barrel at 1547 GMT as investors worried about the turmoil in Greece and fled more growth-sensitive assets. * June U.S. RBOB gasoline futures in New York were down 0.8 percent at $2.8975 a gallon around the same time. * RBOB's crack to U.S. crude futures RB-CL1=R was trading at $28.94 a barrel, down from $30.59 a barrel on Wednesday. NAPHTHA NAF-C-NWE * One naphtha cargo traded in the window at $873 a tonne cif NWE, with Vitol selling to Glencore for May 27-31 dates. * This was down from Tuesday's trade at $884 a tonne cif NWE for May 31 to June 4. * A naphtha broker said that in the short-term the northwest Europe market was quite well-balanced and cracks had moved up about $1 since Wednesday. "However, the market is likely to turn down again soon as cargoes start to build again," he said. * The refining margin was at about minus $10.32 a barrel, according to Reuters' calculations.

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