A substantial petrol price rise is expected to increase the cost of living for earthquake-hit Christchurch residents in the coming days.

Oil prices rose from US$105 to US$115 a barrel amid a political crisis in key supply country Libya.

Petrol companies have withheld a resulting New Zealand price rise in the wake of the 6.3 magnitude quake that hit Christchurch on Tuesday.

Caltex spokeswoman Sharon Buckland says the decision to delay the rise was to avoid putting a further burden on the city.

"This is part of our contribution.

"The price should have gone up. We made a decision this week to hold it where it is.

"It just wasn't the right time."

The company is now under a "great deal" of pressure to raise its petrol price, she says.

She would not say whether it was considering keeping Christchurch prices at their current level and raising them in the rest of New Zealand.

BP spokeswoman Di Papadopoulos says her company also decided against raising prices in the midst of a trying time for Christchurch and New Zealand.

But it will eventually cave to rising international cost pressures, she says.

"The pressure is on us. We're doing our best to shield it from motorists. But it's not a sustainable position, so sooner or later something is going to change."

Petrol prices are being reviewed on "at least" a daily basis, Ms Papadopoulos says.

AA petrol watch spokesman Mark Stockdale is advising motorists to fill up as soon as possible to avoid being hit with the price rise.

"Ten dollars is a substantial increase. If you're running low on fuel, now would be a good time to fill up."

Italian company Eni SpA, which accounts for most Libyan oil operations, suspended production this week - driving up crude prices worldwide.