The survey, which took 475km of driving over two days of last week, revealed some sharp price differences on an area-by-area basis.
Of 162 stations visited on the Tuesday and Wednesday, 53 were found to be discounting 91-octane petrol below 205c a litre.
Although Otara had the cheapest petrol, West Auckland had the highest proportion of discounting stations, with 21 of 32 surveyed charging less than 205c a litre.
But residents of the North Shore and Hibiscus Coast were missing out on deals seen in the south and west, which also tend to enjoy lower prices than those on the Auckland isthmus, although discounting is still alive on Dominion Rd and in Kingsland.
Most northern areas appeared dependent on the standard prices set by the larger oil companies, although that of 91-octane petrol - which accounts for almost 80 per cent of sales - fell by 4c a litre from 212.9c towards the beginning of the survey.
Gull general manager Dave Bodger said that was probably because his company did not have much of a foot-hold there, apart from in Greville Rd, which had seen several others match its 91-octane price of 202.9c.
"What you have seen is that everybody can be really cheap when Gull's in the neighbourhood, but the eastern side of the Shore is 208.9c to a man."
There was no variation in 91-octane petrol sales on the Hibiscus Coast, which was being offered by all eight stations visited by the Herald for 208.9c, even though one cheekily had a board on display announcing: "Discounted fuel here now."
That was probably more a reference to supermarket discount vouchers which motorists rely on for savings.
But in Pukekohe, where an unattended self-service Gull station which opened in October was selling petrol for 199.9c a litre, staff of three other stations were trying to hold their own at 203.9c.
BP, which led last week's move to reduce national prices, was ironically found by the survey to be the least competitive industry player in the Auckland market, although it insists the quality of its fuel is second to none and it will compete strongly on price "where and when we are able".
That message was probably lost on motorists tanking up on the region's cheapest petrol in East Tamaki Rd for 11c less than the new standard, to which Z (formerly Shell) soon followed BP at many of its stations.
Although some Z outlets were discounting below 205c a litre in Auckland, and a BP station was slugging it out with the fiercest of the Henderson discounters at 199.9c, their two brands were generally being undercut.
Only three of 34 BP stations were selling 91-octane petrol below 205c a litre, compared with 17 of 35 Mobil outlets and all 13 Gull sites.
Of 37 Z sites visited, eight were discounting below that level, as were eight of 25 Caltex stations. Although motorists in Manurewa were pleased to watch the advertised price at a Z station tumble by 5c to 203.9c a litre as they headed home from work, one woman said she was putting only as much petrol in her car as would get her to Otara for her regular fill-up.
BP spokesman Jonty Mills said the Herald's survey may have been "distorted" by the brand's price reduction last week, as that typically meant re-setting what was charged at all its company-owned sites nationwide.
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