Delhi, Mumbai world's cheapest cities - survey

People walk at a seafront promenade in the evening at the Nariman Point financial area in south Mumbai March 15, 2012.

ZURICH (Reuters) - Oslo is the most expensive city in the world, ahead of Zurich and Tokyo, but the well-paid residents of the Swiss financial hub enjoy the greatest purchasing power, according to a study released on Friday. The cheapest places to live were Delhi and Mumbai.

The annual survey of 72 cities by Swiss bank UBS(UBSN.VX) found its own hometown had the world's highest average wages and the biggest purchasing power.

The study examined the price of a basket of 122 goods and services, adjusted for currency fluctuations. The cost of living index was calculated by dividing the price of goods by the weighted net hourly wage in 15 sectors.

"In Tokyo it takes nine minutes of work to earn enough to buy a Big Mac, while in Nairobi it takes 84 minutes," it said.

Zurich residents must work 13 minutes for the hamburger, but other goods were relatively cheaper than in Tokyo, putting the Swiss city top of the purchasing power index.

"Workers in Zurich can buy an iPhone after 22 hours work; in Manila, by contrast, it takes around 20 times longer," UBS said.

Workers had to toil 42 minutes in Istanbul and 29 minutes in Shanghai for a Big Mac, while in New York and Hong Kong just 10 minutes were required.

The cheapest places to live were Delhi and Mumbai. New York was the sixth most expensive, Moscow came in at number 40 and Shanghai at 49.

The survey also looked at working hours and found the shortest were in Paris, Lyon and Copenhagen. Workers in Asia, Africa, the Middle East and South America toil the longest, at over 2,000 hours per year, it found.

(Reporting by Catherine Bosley; Editing by Robin Pomeroy)