World oil prices have topped $30 a barrel for the first time since the 1991 Gulf War. The price rise followed rejection by the Organisation of Petroleum Exporting Countries of a US request to increase collective output by 500,000 barrels a day. The Opec countries did not observe an undertaking they gave in March to implement the increase automatically if a basket of crude prices exceeded $28 a barrel, as happened last week. Instead, they deferred a decision on raising production to a meeting of oil ministers in Vienna on 21 June. The latest hike has heightened concern that the rising prices will hit producer input costs and spur inflation.