Australia's oil imports have collapsed under the weight of higher prices and changes in consumer behaviour.
Trade figures released yesterday show just 1.6 billion litres were imported in May, well down on the long-term average of 2 billion litres per month.
May volumes were down 28 per cent on those imported a year earlier.
The change gives heart to those who have claimed the higher prices that will flow from Australia's planned emissions trading scheme will cut greenhouse gas emissions.
The claim has been contested by the Coalition, whose environment spokesman Greg Hunt has asked how ''whacking a great new 20c tax'' on petrol would cut emissions.
''We have serious reservations and scepticism about petrol tax, given that prices have increased four-fold in the last decade and petrol volume hasn't changed at all,'' Mr Hunt said earlier.
The May plunge in oil imports was the biggest annual decline in four years.
It is consistent with other information showing the number of litres of oil bought per person and the number of kilometres driven has been falling.
Westpac Economist Matthew Hassan has calculated in the three years since the oil price began to climb the typical amount spent on petrol jumped from $13.50 a week to $16.90 while the number of litres bought fell from 13.5 litres to 12.9 a week.
The average distance driven per car fell from 14,600km a year to 13,800km in the five years to 2006.
The results echo those in the United States, where in November the number of cars on roads slipped below the level of a year ago.
Latest figures for March show US drivers travelled 17.7 fewer kilometres than a year before.
The 4.3 per cent drop is the biggest-ever year-over-year drop in distance driven.
The Wall Street Journal labelled the phenomenon a ''tipping point'', where price increases have become severe enough to have an effect.
University of California, Davis, economist Christopher Knittel told the Journal, ''What we are seeing now is prices have been high for a while and consumers have become convinced high prices are here to stay.
''That has given them time to make changes, such as the car they buy.
''That has larger effects than, well, I'm just not going to drive to the mall this week.''
CommSec's chief equities economist Craig James said while oil imports had been slowing for six months, the size of the May decline showed Australians had dramatically changed their behaviour.
Mr James said, ''Fewer trips are being made in the car, more people are walking to the shops and using public transport and transport operators are making sure they fill gaps in loads to make less trips''.
The change had been anticipated by the head of the government's climate change review Professor Ross Garnaut.
He told The Canberra Times earlier this month he expected the current ''exceptionally high fossil fuel prices'' to have a strong effect in cutting emissions by themselves.
So strong would be the effect that an emissions trading scheme might now not be needed for Australia to meet the 2012 emission targets imposed on it under the Kyoto Protocol.
''We probably were in a position where we were going to more or less meet our Kyoto targets but now we will be more or less under,'' Professor Garnaut said.
He suggested that when the scheme is introduced in 2010, the price of emissions permits be fixed rather than floating for the first two years to avoid the price of the permits falling to zero.
Petrol prices hit record highs of almost $1.72 a litre in Sydney, Melbourne and Adelaide yesterday.
Prices at some service stations in the three cities reached 171.9c per litre yesterday afternoon.
In Sydney, the spike meant a price jump of up to 20c a litre at some outlets since yesterday morning.