A YEAR-long investigation of Australia's free trade agreements has found they are often nothing of the kind.

The Productivity Commission has told the government there is little evidence to suggest Australia's six free-trade agreements have produced ''substantial commercial benefits''.

Some may have actually reduced trade by introducing complex rules that make it difficult to sell goods made with products imported from countries not in the agreements.

The extra cost imposed by these ''rules of origin'' could amount to 8 per cent of the value of each export shipment.

Copyright provisions inserted in the US-Australia Free Trade Agreement could eventually cost Australia as much as $88 million per year as the nation pays an extra 25 per cent each year in net royalty payments, ''not just to US copyright holders, but to all copyright holders''.