Boston’s office market is nearing bottom, but vacancy in the city will top 15 percent, and sustained positive activity remains years away, the head of Colliers Meredith & Grew’s brokerage unit predicted this morning.

Speaking at a breakfast for tenants, Ronald K. Perry said the pace of leasing activity has accelerated greatly over the last 90 days.

"We’re starting to see more happening," he said, noting that leasing velocity in the third quarter topped what the city had seen in the first half of 2009.

He said the city will likely log another 1 million square feet of activity in the fourth quarter, to close the year at 3.5 million square feet worth of deals. The city normally does 5 million square feet in a year.

"We’re seeing tenants and landlords coming together," Perry said. "That will continue through the end of the year, and into 2010."

Boston’s office market has had more than 1.1 million square feet in negative absorption through the first 9 months of 2009. Meredith & Grew is projecting another 500,000 to 800,000 square feet of negative absorption through the end of 2010, before gains return in 2011. In 2011, the brokerage is forecasting a modest gain of 250,000 square feet; it sees more robust activity in 2012, predicting 750,000 square-feet of positive absorption.

Vacancy, which currently stands at 13 percent, will rise to 15.5 percent in 2011, with the delivery of Russia Wharf and Fan Pier, and then fall in 2012.

"The environment will be conducive to tenants making deals," Perry said.

He said tenants are using a growing number of options to put pressure on their current landlords; that holds true for both small and large tenants.

For example, both Sullivan & Worcester and JP Morgan were able to extract concessions from their current landlords by shopping the market, and then entering into blend-and-extend renewals. Sullivan & Worcester is doing a total rehab job on its 120,000 square-feet of space at Equity Office’s One Post Office Square.

Kevin Charleston, executive vice president and CFO of Loomis, Sayles, & Co., said his firm is currently shopping for 200,000 square-feet, even though its lease at One Financial Center doesn’t roll until 2015. It has a lease opt-out clause, and in the current market, "We have an opportunity for cost certainty for the next 12 to 15 years." He added, "I was surprised at how quickly viable alternatives emerged."