Car manufacturers are concerned about an increase in the price of diesel, a fuel which is not covered by the Australian Competition and Consumer Commission (ACCC) investigation.
Diesel has traditionally been cheaper than petrol, but is now up to 20 cents a litre more expensive.
Andrew McKeller from the Chamber of Automotive Industries is suspicious of the trend.
"It's curious to see that the differential between those two products has increased in the way that it has in recent weeks," he said.
"There is some concern, at a time when unleaded petrol prices are under scrutiny, that refiners may be building margins in terms of diesel prices." © 2007 Australian Broadcasting Corporation
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