The next year-and-a-half could mark potentially momentous migrations of monstrous suburban tenants with the might to move markets, according to a new report from Colliers International.

While the vacancy rate in the suburban Boston office and R&D market combined shows those properties are 21.5 percent empty, there are seven companies in those areas that have potential requirements in the next 12 to 18 months for up to 2.86 million square feet.

The TJX Cos. are in testing the waters to move its headquarters to new digs, which alone would need to accommodate about 1 million square feet. And as Banker & Tradesman was first to report, most brokers point to the 109-acre former Hewlett-Packard site in Marlborough, which Framingham-based Atlantic Management recently purchased for about $9 million, as the ideal location.

But they’re not the only titanic tenant that could need space if they choose to move when their leases expire. The largest include Keurig, the Reading-based single cup coffee company, could be looking to relocate its headquarters to 500,000 square feet along Route 128 North. NetApp, a computer software and services firm with offices in Waltham, could be looking to occupy 400,000 square feet near the intersection or Route 128 and the Mass Pike. And Kronos, the computer software company headquartered in Chelmsford, is contemplating a move to 350,000 square feet in the Interstate 495 North market.

That kind of leasing velocity could really put a needed burst of energy into the suburban markets. At the close of the third quarter, the suburban Boston office and R&D market is statistically flat
with a combined vacancy rate of 21.5 percent, compared to 21.2 percent at the end of 2010.
The suburban office and R&D market totals 128 million square feet, with performance and product varying from one submarket to the next. The Route 128 submarkets combine for a 19 percent vacancy rate, and the three I-495 submarkets together are 26.3 vacant.

The Downtown Boston office market’s vacancy rate dropped to 15.8 percent during the third quarter from 16.6 percent at the beginning of the year thanks to 322,000 square feet of positive absorption, according to Colliers.