The oil price plunge has triggered a string of bankruptcies, debt defaults and rescue measures to save companies nearing collapse, with almost two dozen oil and gas groups now under stress. A 40 per cent slide in Brent crude prices from a peak of $115 a barrel last June, has put smaller, cash-strapped producers in financial trouble, according to City analysts, with up to a quarter of a million barrels a day of oil supply at risk of being curtailed.