Opec on Tuesday pledged to cut oil output by 10 per cent, in a bid to prop up prices before the summer, when demand in its largest markets falls steeply. The powerful 11-country oil cartel, meeting in Algiers, resolved to stop cheating on its 24.5m barrel a day quota immediately, a move that would cut output by 1.5m barrels a day. Opec's 10 active members - Iraq's struggling industry is not subject to the quota - then intend to reduce their quota on April 1 by a further 1m barrels a day to 23.5m. Much of the reduction would have...