CRUDE oil prices tumbled more than 8% on Wednesday amid indications that Iran will back plans by the Organisation of Petroleum Exporting Countries (Opec) to raise production from April 1. At the New York Mercantile Exchange (NYMEX), April delivery crude oil futures settled at $31,26 per barrel, falling $2,87 or 8,4%on the day. The fall comes one day after the contract soared to its highest close since November 26, 1990, three months after Iraq invaded Kuwait and touched off the Gulf War.