Luanda in Angola is the world's most expensive city for expats for the second year running, according to Mercer's 2011 Cost of Living Survey.

Tokyo remains in second position and N'Djamena in Chad in third place.Moscow follows in fourth position with Geneva in fifth and Osaka in sixth. Zurich jumps one position to rank seventh, while Hong Kong drops down to ninth.

New entries in the top 10 list of the costliest cities in the world are Singapore (8), up from 11, and São Paolo (10), which has jumped 11 places since the 2010 ranking. Karachi (214) is ranked as the world's least expensive city, and the survey found that Luanda, in top place, is more than three times as costly as Karachi.

"During the period of data collection for this year's survey the world witnessed an incredible number of natural disasters and political upheavals that have all affected the lives of expatriate employees to some extent. Currency fluctuations and the impact of inflation on goods and services - petrol in particular - have led to some reorganisation of the ranking," said Nathalie Constantin-Métral of Mercer.

"In Africa the picture is patchy with the limited availability of accommodation leading to increased living costs in some key cities, while in most Western European cities the cost of living for expatriates has remained relatively stable over the last 12 months," siad Constantin-Métral. "However, many of the region's cities have still dropped in the ranking. In large, this is because all cities are compared to New York and price increases there have been more significant than in most European cities. Some reduction in accommodation costs, due to the economic downturn, has also been behind changes in rankings for select European cities - most notably Athens and Barcelona."

Down one place from last year, London (18) is the UK's most expensive city, followed by Aberdeen (144), Glasgow (148) and Birmingham (150). Belfast (178) is ranked as the UK's least expensive city.

Europe, the Middle East and Africa

Only three European cities remain in the top 10 list of most expensive cities. Moscow (4) is still the most costly European city on the list, followed by Geneva (5) and Zurich (7). Oslo (15) is down four places from last year, whereas Bern (16) has jumped six and Copenhagen dropped seven places from 10 to 17. London (18) is followed by Milan (25) and Paris (27) both down 10 places from last year. St. Petersburg ranks 29, followed by Rome (34) and Vienna (36). Up from 76 in 2010, Stockholm (39) has seen one of the most dramatic changes in the region - mainly due to a considerable strengthening of the local currency against the US dollar.