Oil prices slumped below $70 a barrel this evening, hit by falling stock markets, a rising US dollar and concerns about demand in China, the world's second biggest energy consuming nation. Brent crude slid $2.58 to $68.74 a barrel, while US crude shed $2.37 to $69.67.

A stronger US currency makes dollar-priced oil more expensive for holders of weaker currencies and tends to dampen demand - and prices.

Meanwhile crude oil prices are unlikely to rise significantly this year, unless there are 'clear signals' the world economy has escaped from the worst downturn in decades, energy consultancy CGES said.

The influential Centre for Global Energy Studies added in a monthly report that high crude stockpiles were still holding the market back.

CGES added that the Organisation of Petroleum Exporting Countries (OPEC), which pumps 40% of world oil supplies, was satisfied with the current level of oil prices. Earlier this month, OPEC decided to maintain its production levels as the cartel deemed the market to be 'oversupplied'.

But the head of French oil giant Total said in an interview that oil prices risked rebounding far above $100 unless there was greater investment in energy exploration. Total chief executive Christophe de Margerie also told the BBC that oil prices at their current level of about $70 a barrel were too low to support long-term investment by his company.