It turns out competition between petrol companies doesn't extend to premium fuel.

Pahoia resident Bill Murphy regularly fills up at BP Te Puna. He uses premium because it's better for his car – but he's concerned it's priced far above regular 91.

'Modern cars will adapt to lower octane levels,” says Bill.

'But the performance is definitely impacted using regular, and many manufacturers recommend 95 at a minimum.”

He wants to see premium listed on the price boards that sit outside petrol stations.

'Being made to advertise the price of 91 leads to competition, causing the price to drop. So I'd like to see similar price competition around premium.”

AA senior policy analyst Mark Stockdale says they've been talking about this issue for a long time.

'Some motorists have been complaining because they see 91 advertised at a lower price, and assume premium is also similarly priced. However, upon driving up to the pump they find the price of 95/98 to be substantially more than they anticipated.”

Normally the difference between 91 and 95 is nine cents per litre. But often it can be 30 or 40 cents more.

'If you're discounting 91 by 30 cents from the national price, as some stations do, but they're not discounting premium, then suddenly you've got that price gap,” says Mark.

He says Tauranga has aggressive local price competition – but the discounting often only applies to 91 and diesel.

'Some brands will discount premium, but unless you go in and check it at the pump, motorists have no way of knowing.”

'We think the lack of discounting on premium petrol is unfair. If a station is discounting 91 and diesel, they should also be discounting premium petrol.”

He also believes compelling petrol stations to advertise their premium price would lead to competition.

'They wouldn't want to display a price difference of 40 or 50 cents a litre.”

BP corporate and external affairs manager Leigh Taylor says their premium brands are just that – premium – so they don't discount them.

'Compared to BP Unleaded 91, these fuels offer power, responsiveness and efficiency benefits. BP premium fuels include Active technology which has been developed to also bring our customers engine-cleaning and protecting benefits.

She says BP displays pricing of all fuel grades at the pump, as required by government regulations.

'The information displayed on the boards outside our stations is at our discretion, and because there isn't space to include all prices, we display the price of BP Regular 91, our most popular product.”