BP, the UK energy group, has discovered a “giant” oilfield in the Gulf of Mexico that shows a new frontier opening up for US oil production.

The Tiber field, in more than 1,200m of water about 250 miles south-east of Houston, is one of the biggest discoveries in recent years. It is thought to hold at least 3bn barrels of oil – of which about 500m would be recoverable with today’s technology – and could be significantly larger.