The survey, which ranks both the most expensive and the fastest growing (in terms of rental rates) cities, proves the real estate industry is really becoming a global market place. "If you look at the markets that are rising rapidly, you might ask what is the connection between these markets," Caswell says, citing places like Sofia, Bulgaria; New Delhi; Moscow; Warsaw and Abu Dhabi, UAE. "There are a lot of these different trading partners that are causing a worldwide synchronized expansion."

The proof of the pudding will be when the wave begins to fall. "This is starting to be less of an anomaly and more of a trend," Caswell says. "To be a true trend we will have to see [the cities] stay in synch not just through a rise but through a fall."

According to the report, London's West End holds the title of most expensive city, with rents at $241.22 per sf. This is followed by London's CBD, at $165.72 per sf, Tokyo's inner central at $162.09 per sf, Tokyo's outer central at $143.52 per sf and Mumbia, India at $138.41 per sf. The only US city to make the top 50 most expensive cities list was Midtown Manhattan. This part of the city ranked 21 with an average rental rate of $69.44 per sf.

Abu Dhabi saw a 102.9% growth in rental rates in the last 12 months, which gave it the first position on the list of the 50 fastest growing markets. New Delhi; Sofia; Edmonton, Canada; and Singapore took the next four slots, respectively. West Palm Beach ranked seventh after growing 45%, and Downtown Manhattan took the 10th spot with 42.8% growth. Other US locations to make the list include, Midtown New York (19), Boston (31), Denver (35), Seattle (36), San Francisco (37), Fort Lauderdale (38), Honolulu (41), Los Angeles (42), Miami (48) and Phoenix (49). "Those markets that have a more diverse economy are leading the way in the expansion," Caswell says. "But those with just single industries, like Detroit, are still waiting."

The Global Market Rents survey has compiled all the latest data from across the globe, including the most recent Q1 statistics, according to Caswell. The report, which was initially published in January and August, will now be disseminated in May and November to better reflect the market conditions and more accurately track change.