The Road Transport Forum says lower fuel prices won't mean a drop in freight costs just yet.
Petrol has dropped 10 cents a litre in the past 10 days, and the cost of diesel was cut by 3 cents a litre on Tuesday.
Road Transport Forum chief executive Tony Friedlander says lower fuel prices will help the transport industry, but will not be passed onto businesses until freight volumes increase.
"The price of fuel would have to drop substantially to have an impact." he says.
"Because of a drop-off in freight volumes the turnover of transport companies is well down but their costs remain high."
A UBS senior economist, Robin Clements, says speculation that the world economy would improve had driven oil prices up, but they're now being corrected because productivity is still low.
Automobile Association policy analyst Mark Stockdale says international prices will continue to fall, and petrol companies should keep passing on the benefits.