"It's a policy issue," said CEO Brian Molefe, whose company is about to embark on a R300-billion capital investment programme of which a large chunk will be invested in rail infrastructure for the export of coal.

Classifying coal as a "strategic resource" was mooted by Public Enterprises Minister Malusi Gigaba. The ANC is considering the suggestion, which could place a cap on coal exports.

Eskom last week welcomed the proposal. The power generator hopes it will ensure its coal supply and put downward pressure on prices.

The volumes of export coal increased by 8.8% in the past year to 67.7million tons - accounting for about a third of all Transnet's freight. It is expected to reach 75million tons this year.

Mining companies have protested against the coal classification, saying it will hurt exports and lower tax revenue.

Some also claim it would be a disincentive to investment in the local coal mining industry. These concerns were dismissed yesterday at Transnet's results presentation.

"Will South Africa consume all its own coal?" asked Molefe. ''If we do, we'll change our business model."