It means predictions the Reserve Bank will cut rates early in 2015 may have been premature, despite rising unemployment and a still-weak economic outlook for next year.

Australian petrol prices fell to a four-year low this month – in the week before Christmas – at 128.4 cents a litre on average, with the decline over the last four weeks representing the biggest fall for an equivalent period in six years.

It means the average Australian household is saving roughly $32 a month on petrol, compared to a year ago, helping to boost spending power at a crucial time for retailers.

A number of Australia's biggest banks – including Westpac and Deutsche Bank – have recently predicted the Reserve Bank will have to slash the cash rate by 0.5 percentage points next year, with the first 0.25 percentage point drop coming in the first few months of 2015, in the face of rising unemployment and weak growth.

If that occurred, it would see the cash rate fall from a historic low 2.5 per cent to just 2 per cent.

But RBA governor Glenn Stevens, in a recent interview with Fairfax Media, has indicated he would be happy to leave rates where they are for the time being, though he would like to see the dollar fall further towards US75 cents.

In the last few weeks the dollar has fallen from roughly US85cents to US80.89 cents, its weakest since June 2010.

Economists say hopes of another rate cut early next year appear dashed after the US economy recorded surprisingly strong economic growth this week.

New figures show the US has been growing at its fastest rate since 2003, with third-quarter GDP hitting an annualised 5 per cent, up from an estimated 3.9 per cent, thanks to a big pick-up in the pace of consumption growth.

US economists say the US Federal Reserve may now be forced to consider whether they will need to raise rates before the middle of 2015, and if that were to occur Governor Stevens' decision to leave Australia's cash rate on hold would have more support.

"The Australian dollar is doing the Reserve Bank's work for it," Deloitte Access Economics director Chris Richardson said.

"If the RBA's worried about the pace of growth in Australia, and it should be, it's going to be happy with lower petrol prices, because it's like a specific interest rate cut for businesses and families, and it's going to be happy with the lower Australian dollar, which is like an interest rate cut for companies that compete with imports and those companies that export," he said.

"There have been big swings in fashion over the past year, early in 2014 there was a fashion about rates rising by mid-year, but we always said the first rate rise wasn't until the end of 2015 and we've never changed."

Australian consumers have spent a record $45 billion in the six weeks before Christmas, with $2 billion more expected on Boxing Day sales, as they enjoy a reprieve at the petrol pump.

Big retailers have welcomed the figures, after consumer sentiment fell by a massive 5.7 per cent in December, to 91.1 points, due to ongoing disillusionment with the federal budget and concerns about a weak economy.

Anything under 100 means the number of people who are pessimistic about the state of the economy outweigh the number of optimists.

But Commsec Chief Economist Craig James says consumers have benefited from the large fall in petrol prices, with the $32 fall in the cost of petrol this month being equivalent to a 0.25 percentage point rate cut on a $200,000 mortgage.

"The fall in the petrol price is acting like a de-facto rate cut," Mr James said.

"Lower petrol prices and a lower Aussie dollar mean that the Reserve Bank can leave rates steady."