Singapore has been named the world's most expensive city for the third year running.

According to rankings given by the Economist Intelligence Unit (EIU), Zurich and Hong Kong came in at the second and third places.

Mega metropolises London and New York were ranked at the sixth and seventh positions, respectively.

The cheapest in a list of 133 cities were Lusaka, the capital of Zambia. The EIU ranks cities by comparing their cost of living against that of New York.

Singapore had a score of 116 while Zurich and Hong Kong were close behind with 114, according to the EIU's Worldwide Cost of Living report.

Chief among factors that made Singapore the costliest city in the world was the cost of transportation, the report showed.

Buying and running a car in Singapore was 2.7 times costlier than New York, the study found.

Researchers said economic changes like the commodity collapse and the currency devaluations were factors that made 2015 highly volatile.

"In nearly 17 years of working on this survey I can't recall a year as volatile as 2015," one of the editors of the survey said, according to BBC.

"Falling commodity prices have created deflationary pressures in some countries, but in others currency weakness caused by these falls has led to spiralling inflation."