While the largest metros predictably record the most transaction volume, a few surprises made the cut of the top 10 most active apartment markets so far this year, according to data provided by Real Capital Analytics.

Manhattan tops the list as the most active apartment market, with more than $1.8 billion in sales volume for the first six months of the year. Washington, D.C. (and its Virginia suburbs) and Los Angeles came in behind Manhattan with $1.5 billion each.

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Yet, while Manhattan tops the list, it saw a 33 percent drop in transaction volume compared to the first half of 2012. Other markets on the list had significant increases, with the Washington, D.C. (Virginia area) up more than 100 percent over the first half of last year. And the Maryland suburbs of Washington, D.C. were no slouch either, coming in at 12th with $675 million in sales in the first six months of the year.

Other markets with significant increases that didn't make the cut include Las Vegas, the 15th most active market with $507 million in sales, it's highest ranking in more than eight years.

Surprisingly, Orlando made the top 10, it's highest ranking in at least eight years, up from the 28th most active market last year, with a 144 percent increase.

Top 10 Apartment Markets This Year
1. Manhattan: $1.8 billion
2. Washington, D.C. area: $1.5 billion
2. Los Angeles: $1.5 billion
3. Dallas: $1.356 billion
4.Houston: $1.351 billion
5. Atlanta: $1.315 billion
6. Phoenix: $975 million
7. Chicago: $911 million
8. Denver: $840 million
9. Orlando: $809 million
10. Seattle: $767 million

Lindsay Machak is an assistant editor for Multifamily Executive. Connect with her on Twitter @LMachak.