The Organisation of the Petroleum Exporting Countries, the oil cartel, has raised the price of its own oil to the highest level in a year, while publicly promising to tackle the high cost of oil at this week's meeting in Vienna.

Emboldened by strong demand and a high oil price that has yet to have a significant impact on global economic growth, several of Opec's biggest Middle Eastern producers last week further increased the prices they charge US and European traders and refiners for their oil.