Z Energy admits faulty fuel, which is causing some motorists to run out while driving, could be more widespread than initially reported.

The company says a batch of active sulphur content fuel was more widely distributed and affected more vehicle types, than first thought.

It says it's received less than a handful of calls about the issue from outside Auckland. These have been from Hamilton, Northland and Hawke's Bay.

"We want to be accurate in our view of the issue," Z Energy says in a Twitter exchange. "Every case will be investigated fully, and customers compensated if it's found the fuel could be at fault."

High levels of sulphur can trick some vehicles' engine fuel senders, resulting in a quarter tank gauge reading when actual fuel levels are lower.

The problem was initially reported to be confined to Auckland.

Fuel companies spokeswoman Leigh Taylor says faulty fuel was supplied in November and December, and they are looking into its distribution.

"There's a group of technical experts working on this from across the industry," she says.

"They are investigating the supply chain. It's very complex. They are investigating that in its entirety to figure out exactly how this has happened."