''It depends on when, where and how and it depends on how the market is.''
Waitomo Petroleum spokeswoman Greta Shirley said the company would open a fuel stop in central Christchurch towards the end of the year.
''We are also actively looking at other sites. Watch this space.''
The company has 50 fuel stops in the North Island and opened a new site in Wellington on May 14.
Both Waitomo and Gull have previously been unable to access the Wellington market but are now expanding into the capital.
Another fuel discounter Nelson-based NPD, has also been growing around the South Island. The company has more than 50 sites around the South Island.
AA petrol watch spokesman Mark Stockdale said for a long time the South Island had missed out on discounted fuel but those days were ending.
''With their no-frills brands and low overheads these companies can offer lower prices that can range from 20c a litre and sometimes 30c or more cheaper.''
The expansion comes as a new terminal is being built at PrimePort Timaru by Tahitian-based company Timaru Oil Services which is due for completion next year.
''The terminal is not owned by the existing import companies BP, Z and Mobil and this independence will increase confidence to Gull and others,'' Stockdale said.
''Now with the new terminal looking for customers it will shake up competition among the wholesalers which will trickle down to retailers.''
South Canterbury Chamber of Commerce chief executive Wendy Smith said on a number of occasions with a variation in fuel pricing across New Zealand, South Canterbury appeared to have been on the wrong end, and so the arrival of Gull would be welcomed.
''Petrol is a fixed cost for any business and competition is always a good thing.''
The new terminal being built at PrimePort was an indicator of the strength of the South Canterbury economy, she said.