Motorists have gained their third petrol price cut in eight days, but the Automobile Association believes there is room for a bigger drop for diesel users.
The oil companies yesterday cut both petrol and diesel prices by 4c a litre, earning praise from AA spokesman Mark Stockdale for acting promptly to pass on cost reductions.
But he saw no reason why, after a period in which petrol dropped by 12c a litre, diesel was just 8c cheaper than on Thursday last week.
Mr Stockdale said industry data obtained by the AA indicated that oil companies were making a big enough margin on diesel for them to have cut that fuel by 4c on Monday, a day when they dropped petrol prices only.
The big oil companies were selling 91-octane petrol at main centre pumps last night for 206.9c a litre, and diesel for 183.9c, prices which minnow supplier Gull was able to undercut by 1c.
BP spokeswoman Diana Stretch rejected the AA claim, saying the cost of importing refined petrol had dropped by $23 a barrel since early last week, to $167, compared with a $17 reduction for diesel - to $218.
Despite the higher cost of refined diesel, it is cheaper than petrol at the pumps because its retail price does not include taxes paid separately as road user charges.