Mobil says a variety of issues led to the lack of unleaded petrol supplies in parts of the South Island.

Mobil service stations in Canterbury and Otago are running out of unleaded fuel and it could be more than two weeks for stocks in those areas to return to normal.

Mobil Oil New Zealand has confirmed that over the next week or so there will be periods when Mobil stations in Christchurch, Timaru and Dunedin will not have regular or premium unleaded fuel.

Mobil said unleaded petrol stocks for Christchurch customers should be fully restored by Waitangi Day, but it could take up to a week to resolve supply problems in Timaru, and normal stocks should again be available in the Dunedin region by February 16 to 20.

It said Mobil stations in other parts of the South Island were not experiencing supply problems.

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BP, Z Energy and Gull confirmed their stations were not affected.

Mobil's lead company manager Andrew McNaught​ said the issues related to unforeseen shipping delays and lack of port storage in Dunedin.

The company had also received less gasoline that planned from Refining NZ in November and December, and that had affected its ability to meet greater than anticipated demand across the South Island over Christmas and the New Year.

McNaught​ apologised to customers for any inconvenience and said the company was actively working on alternative supply arrangements to minimise the impact.

"Where possible, we have increased trucking from other terminals where supply has not being impacted, as well as identifying other supply sources."

He said efforts to improve Mobil's long-term capacity in the South Island included the construction of two new storage tanks for unleaded fuel and diesel at the Lyttelton port terminal, with those tanks due for completion early next year.