Kiwis appear to be paying too much at the petrol pump and the business watchdog is likely to gain new powers to investigate, the Energy and Resources Minister says.

An updated Ministry of Business, Innovation and Employment-commissioned study into retail fuel pricing is expected today.

Foreshadowing its release, Minister Megan Woods said petrol prices were often different between suburbs within Auckland and typically higher in Wellington and the South Island.

The Commerce Commission was the right authority to investigate those differences, but it needed more powers to compel petrol companies to co-operate, she said.

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"What we are going to do is give the Commerce Commission the market study powers it needs so it can look at the reasons people are paying such wildly different prices around the country," she told Three's The AM Show.

"We've got to get to the bottom of this, people need to know they are paying a fair price when they fill up their car."

Wednesday's report is an update to an MBie study released in July.

That study also found higher petrol prices in Wellington and the South Island may not be reasonable and suggested the Commerce Commission could be empowered to investigate.

- NZN