Diesel has dropped by three cents a litre at Shell, BP, Caltex and Mobil stations, three days after the Automobile Association called for cheaper prices at the pump.

All five petrol companies said the drop was due to a fall in the international price of diesel and had nothing to do with the AA's call for a price drop on Monday.

Shell, BP, Caltex and Mobil all began selling diesel for 101.9 cents a litre, late yesterday afternoon. Gull dropped by four cents and is now two cents cheaper at 99.9 cents a litre.

AA policy analyst Mark Stockdale said the latest drop brings the price of diesel down to where it should be when taking into account the international price of fuel, the cost of importing and the New Zealand dollar exchange rate.

"In fact, things are looking positive with a strong exchange rate possible, if things continue to look up there may be room for [more] movement on petrol and diesel," Mr Stockdale said.

He said the price of diesel could have been dropped by six cents on Monday.

Petrol companies dropped the price of diesel by three cents a litre on Tuesday.

Gull spokesman Graham Stirk said there was no room to drop the price of diesel earlier. Shell spokeswoman Kylie Reeves agreed and suggested that the AA made their calculations using a different method than the petrol companies.

Caltex spokeswoman Sharon Buckland said the AA did not "drive the price of fuel".

"They're entitled to their view but they're not privy to the information we have as a company," Ms Buckland said.

Mobil spokesman Alan Bailey said Mobil dropped its price because of the international price, the exchange rate and the move by competition.

"The AA have a view but I guess we have a different view," Mr Bailey said.

Shell

91 petrol: 158.9 cents a litre

Diesel: 101.9 cents a litre

Caltex

91 petrol: 158.9 cents a litre

Diesel: 101.9 cents a litre

BP

91 petrol: 158.9 cents a litre

Diesel: 101.9 cents a litre

Mobil

91 petrol: 158.9 cents a litre

Diesel: 101.9 cents a litre

Gull

91 petrol: 157.9 cents a litre

Diesel: 99.9 cents a litre