More than 65 per cent of the world's coal production is estimated to be unprofitable as prices for both thermal and coking coal head for their fifth consecutive year of declines.

The estimate, which was provided by commercial intelligence company Wood Mackenzie, applies to both types of coal. It would be even higher if sustaining capital spent by miners on things like engine maintenance was taken into account.

Slowing demand in Asia and an increasingly carbon-conscious world have put pressure on the price of coal. Credit:Bloomberg

The extraordinary estimate illustrates the parlous state of the coal industry, which has been battling slowing demand in Asia and structural challenges surrounding coal's place in an increasingly carbon-conscious world.

The Wood Mackenzie data includes coal mined for export markets and domestic energy supplies around the world.