Total, the French oil company, said on Thursday that oil prices had slipped to within sight of the threshold below which some of its most expensive projects will no longer be commercially viable.

Total’s extra heavy oil sands project in Canada requires an oil price of just below $90 a barrel to achieve a 12.5 per cent internal rate of return, while Total’s developments in the deep waters off Angola need about $70 a barrel, the company revealed in a mid-year presentation. International oil prices on Thursday traded at $102.10 on the New York Mercantile Exchange.