"With the severity of the downturn we saw last year, the obvious trend is very clear," Tamara Kos, EVP for Transwestern's Midwest region, tells GlobeSt.com. "We think vacancy is going to peak at about 15% as more vacancy hits us in the near term because of lease expirations. That probably translates into rental rates and concessions."

Sublease space too increased to more than 4 million square feet during the third quarter, but according to Jones Lang LaSalle's research, the pace at which space is hitting the market has slowed. "Despite the prevalent amount of attractively priced sublease offerings, deal velocity remained below historical norms, with many tenants continuing to opt for extensions in place including short-term renewals," JLL's research report says. It showed that the CBD class A overall gross asking rate has declined by 5% since the beginning of the year, and projects that activity will increase as tenants look to take advantage of market conditions.

"People who have been sitting on the sidelines will come and do some deals in 2010 with what are historically some very attractive rental rates," Kos says. "The last year and a half, a tremendous amount of tenants have held of on making decisions about renewals, expansions or relocations because of uncertainty about their business plans. A number of tenants who had to make decisions chose to do something shorter term - 6 to 24 months - so they had flexibility in the future, and those tenants will be out in the market again in the next 12 to 18 months and this time they might make those longer term decisions."