Sydney and Melbourne no longer rank among the world's 10 most expensive cities, thanks to the weaker Australian dollar.
The currency weakness has pushed down the relative cost of living in Australian cities in a global survey topped by Singapore.
London, New York and Los Angeles have pushed Sydney, Melbourne and Oslo out of the Economist Intelligence Unit's 10 most expensive cities.
Sydney and Melbourne have fallen from 5th and 6th place to 20th and 21st, respectively.
Singapore retained the title of the world's most expensive city for the third year in a row, closely followed by Zurich and Hong Kong in joint second place.
Survey editor Jon Copestake said he could not remember a year as volatile as 2015.
"Falling commodity prices have created deflationary pressures in some countries but in others, currency weakness caused by these falls has led to spiralling inflation," Mr Copestake said in a statement on Thursday.
Only eight of the 133 cities surveyed had unchanged rankings in the past year.
The EIU noted the stronger US dollar and weaker euro have pushed euro zone cities further down the rankings.
The Australian and New Zealand dollars have also weakened significantly from highs of two years ago, making cities in Australasia more affordable to global travellers, it said.
Brisbane has fallen to 49th position and Adelaide to 53rd.
Three years ago Perth ranked as the 11th most expensive city in the world but has now fallen to 56th, just above Bangkok and Hanoi.
Auckland and Wellington have also become cheaper, at 38th and 42nd respectively.
