LONDON, Jan 8 (Reuters) - Gasoline barge prices in Europe rose on Tuesday, boosted by spot demand in the Mediterranean following last week's Skikda refinery fire, and improved demand from the United States. Algeria's Sonatrach issued a prompt tender on Monday for two more cargoes of gasoline by the end of January following a small fire at its Skikda gasoline reformer. Traders said the market had been expecting another tender after the fire broke out at the end of last week. It is not clear when the reformer will be fixed and Sonatrach also has a crude distillation unit (CDU) in turnaround until February. Gasoline is also being supported because of improved demand from the United States, where Motiva is still having trouble with its new 325,000 barrel-per-day (bpd) CDU at its Port Arthur, Texas refinery. Traders said that European gasoline had been moving to the United States over the past week, but at current arbitrage levels they do not expect to see many more cargoes going. Freight rates have picked up in response to demand, which has taken some of the profit out of the equation. Fewer cargoes are also said to be moving to West Africa because of rising freight rates. "The economics don't work right now," one market participant said. The Skikda outage is expected to lead to more naphtha entering the Mediterranean market, but this has had little impact on prices to date, traders said. "People won't notice if there's another 30,000 tonne Skikda cargo to be loaded," one said. "But if it's going to last for a few months, then that will get people's attention." Traders expect the Asian market to absorb some of the surplus naphtha as the arbitrage to the East is wide open, with the spread at about $26 a tonne from the Mediterranean and about $15.75 a tonne from northwest Europe. Asian naphtha crackers are operating at high rates whilst regional refineries are offline for maintenance, so European naphtha is likely to be in demand. GASOLINE * Two barges of benchmark Eurobob traded in the window at $978 a tonne fob ARA, up from $975 a tonne on Monday. * Gunvor sold a barge to Trafigura and Chevron sold a barge to Gunvor. * Some 3,000 tonnes traded ahead of the window at $983 a tonne fob ARA, up from $970-$981 a tonne on Monday. * Total and Gunvor sold to BP and Cargill. The earliest trade came at a premium to the February swap of about $5 a tonne. This was at the lower end of Monday's $4-$8 a tonne range. * Some 6,000 tonnes of premium unleaded gasoline traded at $998-$1,003 a tonne fob ARA, in line with Monday's trades at $1,002 a tonne. * Argos and Trafigura sold the barges to Total, Statoil and Litasco. * At 1643 GMT, Brent crude oil futures were up 54 cents at $111.94 a barrel. * Eurobob's crack to dated Brent was at around $3.23 a barrel, down slightly from around $3.32 a barrel on Monday. * February U.S. RBOB gasoline futures were up 0.47 percent at $2.7904 a gallon. * RBOB's crack to U.S. crude oil futures was trading at around $24.11 a barrel, up from $23.27 a barrel around the same time on Monday. NAPHTHA * One naphtha cargo traded, with Vitol selling to Trafigura at $934 a tonne cif NWE, up a notch from Monday's trades at $929-$933 a tonne. The loading dates were Jan. 26-30. * The prompt naphtha crack was at about minus $7.04 a barrel, weakening from about minus $6.39 on Monday evening.