AA spokesman Mark Stockdale said after a succession of cuts in May and June, petrol had risen by 26c a litre in the past six weeks because of rises in international commodity prices, fuel tax and oil company profit margins.
The price includes a 2c rise in the Government's fuel excise at the beginning of the month, and extra GST which is contributing to a tax take of 90.2c a litre.
Diesel was up last night to 156.9c at Caltex, Z and Mobil and 1c higher at BP outlets, although still well below a record high of 191.9c.
However, Mr Stockdale said import costs for fuel had not risen since the last increase at the pump - 3c last week on a litre - and believed fuel companies could have held the price.
Gull general manager Dave Bodger said his company had managed to keep its prices down through efficiency measures, the benefits of which it was choosing to pass back to motorists rather than "swallowing the profit".
Z spokeswoman Sheena Thomas said the cost of imported fuel had increased by about 30c a litre since July 5, compared with the 26c of retail price rises including higher tax.