Oil prices slipped in Asian trade, falling back after sharp gains overnight made on concerns about unrest in Nigeria, a major exporter, dealers said. At 12.40 pm (0440 GMT), New York's main contract, light sweet crude for delivery in April, was down 32 cents to 62.42 usd a barrel. The contract for delivery in March had jumped 1.22 usd to 61.10 usd a barrel overnight in the US before its expiry. Dave Ernsberger, Asia Oil Director of Platts, said the Nigerian situation, if it continues as it is, will likely have less of an impact on prices this week. "Unless a major escalation occurs it is not likely that crude prices will move much," he said. Yesterday, Nigerian officials sought to negotiate the release of nine foreign workers being held as "human shields" by rebel fighters. The nine oilmen -- three Americans, a Briton, two Egyptians, two Thais and a Filipino -- were seized on Saturday by separatist guerrillas during an attack on energy giant Shell's Forcados oil terminal. Damage to the terminal and surrounding pipelines, combined with fears for the safety of other workers, has forced the firm to cut production by 455,000 barrels of oil per day, equivalent to almost 20 pct of Nigeria's total output. Nigeria, the world's sixth-biggest exporter of oil, produces light, sweet crude, which is easier and cheaper to refine than heavy, sour crude, produced by Saudi Arabia. The market was also keeping an eye on Iran, whose nuclear standoff with the West could lead to a disruption of the country's oil exports. At the same time, traders followed a continuing war of words between US officials and Venezuelan President Hugo Chavez, who has threatened to cut off oil exports to the United States if Washington goes too far in its campaign against him.