Former Prime Minister Tony Abbott was derided for praising coal as "good for humanity,'' given the environmental harm the fossil fuel causes. He may feel partly vindicated after its recent price spike.

The nation's second-largest export product has surged this year, with coking coal up a staggering 240 per cent, and was the star factor behind the narrowest trade deficit in 21 months in September, according to data released on Thursday. And market researcher Capital Economics projects the figures could get even better.

"If coal prices stay at current levels, the deficit could be wiped out in a matter of months,'' said Paul Dales, chief Australia and New Zealand economist at Capital Economics in Sydney. If that happens, it would be Australia's first trade surplus since March 2014. "But that's a very big `if,''' he says.