Shell is asking people in Christchurch to only buy fuel that is needed, while another energy firm says there is enough petrol available in the city.
Caltex says there is no shortage of fuel in Christchurch and motorists should not panic buy.
The company says although Lyttleton Port is closed fuel supplies are being trucked to the city from Timaru.
A spokesperson says the company is worried that panic buying may force some petrol supplies to run out at individual service stations.
She is urging people to fill up only as needed.
BP, Mobil and Shell are operating a limited number of sites as safety inspections continue for closed sites following Tuesday afternoon's magnitude 6.3 earthquake.
One petrol station in Christchurch says it is refusing to sell fuel to the public, and it won't be swayed by people's "sob stories".
Mandy Shuker from the privately-owned Sawyers Arms BP station, says its two underground fuel tanks are low and they are only supplying to the emergency services.
A spokesperson at Greenstone Energy, which runs Shell, Jonathan Hill, says its primary aim is to help emergency services.
He says fuel is available, but the company has noticed a high demand at its petrol stations, and he is asking for people to only purchase what is needed.
However, Mobil says there are no concerns about fuel availability.
Meanwhile, BP says it has reopened some of its 18 service stations, which were closed on Tuesday as a precaution.