THE world's oil producers are wasting more than $50 billion a year of natural gas by burning it off in flares — and adding significantly to the world's greenhouse gas emissions in the process.

A study commissioned by the World Bank and carried out by the US National Oceanic and Atmospheric Administration estimates that, based on satellite photos, 170 billion cubic metres of natural gas went up in oil producers' flares last year.

The bank said the amount was equivalent to 27 per cent of the entire US consumption of natural gas, and 5.5 per cent of global gas output. Had it been sold in the US at 2006 prices, it would have been worth $US40 billion ($A53 billion at 2006 exchange rates).