KEY POINTS:
One petrol company has dropped the price of diesel to less than a dollar for the first time since May, 2007.
The minnow Gull is now selling diesel for 99.9 cents a litre - a drop of three cents this morning.
Gull held out on a petrol price rise yesterday but has since raised petrol prices by 5 cents a litre to 136.9. The price rise is in line with the four main petrol companies yesterday.
Caltex, BP, Shell and Mobil are now selling 91 Unleaded for 137.9 cents a litre and 95 for 142.9, although BP is selling 95 for 143.9. They are all selling diesel for 103.9 cents a litre.
Gull's retail business manager Graham Stirk said the fall in diesel came because there is "a bit of leeway" in the international price.
"Petrol is going up at a far greater rate," Mr Stirk said.
Meanwhile, the Automobile Association has said petrol companies had no choice but to raise the price of petrol yesterday after the international price of petrol climbed last week.
Mr Stockdale said the international price of petrol rose last week, resulting in a fall in margins for petrol companies.
"They haven't adjusted the price of diesel because the [diesel] margin is a little higher," Mr Stockdale said.
He said the weakening of the New Zealand dollar has also caused difficulties because petrol and diesel is traded in US dollars.
"Oil companies work on the basis of a one week lag and they haven't been able to hold out any longer," Mr Stockdale said.
Yesterday, Shell spokeswoman Jackie Maitland said supply had been constrained with the refinery in Whangarei closed for planned maintenance.
She also warned that the 4 cent drop in the New Zealand dollar so far this week had not helped prices going into the future.
Mobil spokesman Alan Bailey said the rise followed a "significant increase" in the regional market price for petrol in US dollars against a weakening New Zealand dollar.
The New Zealand dollar has continued to fall, slipping below 54 cents against the US dollar overnight.
It has recovered slightly since and at 8am this morning was buying US54.02c having dropped from US55.60c at 5pm yesterday.
Caltex spokeswoman Caroline Bland also pointed to the weakening Kiwi.
She said pricing staff had told her that last week's average for the dollar was around 59.45 cents against the US dollar but this week it had gone down to 57.45 cents.
Shell
91 Unleaded: 137.9 cents a litre
V Power: 142.9
Mobil
91 Unleaded: 137.9 cents a litre
95 Ultra: 142.9 cents a litre
Caltex
91: 137.9 cents a litre
95: 142.9 cents a litre
Diesel: 103.9 cents a litre
BP
91 Unleaded: 137.9 cents a litre
95: 143.9 cents a litre
Diesel: 103.9 cents a litre
Gull
91: 131.9 cents a litre*
Regular Plus - a biofuel blend: 129.9
Diesel: 99.9 cents a litre
*Lower at some sites.
