Bank of America, for example, plans to occupy about 500,000 square feet at 110 N. Wacker Dr., a proposed 51-story tower by Riverside Investment & Development and Howard Hughes that was recently approved by the Chicago Plan Commission. And many others have similar needs.

Researchers from NGKF recently found that, over the next few years, tenants needing a total of about 13 million square feet will test the Chicago market. “If I was a betting person, which I am, I would bet that in the next 18 months we will see another class A tower,” says Chodos.

There are a number of options, he adds. Hines, the developer of 444 W. Lake, has a building pad at Wolf Point ready to go, and Tishman Speyer already has a design for a 1.1 million square foot tower at 130 N. Franklin. Another Fulton Market development on the scale of McDonald's new headquarters also remains a possibility.

Beyond that, several windows of opportunity will open between 2021 and 2024, when the leases for several big players will expire. And as tenants this large typically begin their searches four or five years out, downtown developers will soon have to make important decisions.

Chodos believes the quick progress made at the newest trophy properties such as 444 W. Lake and 150 Riverside will boost these developers' confidence. “These buildings have all opened substantially leased,” and the spaces opened up by these moves were also filled quickly.

Even buildings which opened in the trough of the recession, he points out, such as 353 N. Clark St. and 300 N. LaSalle, were occupied relatively quickly. The pair subsequently sold for the record-breaking prices of $715 million and $850 million, respectively.

That's a sign of both the market's tremendous vitality, and the disciplined approach taken by developers. “We haven't experienced massive overbuilding.”

CHICAGO—Over the next year or so, landlords and developers in Chicago's downtown office market will play very close attention to the amount of new space absorbed by users. Several class A towers were recently opened, and if all that space gets quickly absorbed, it will almost certainly help push developers to launch additional projects that will transform the city's skyline.

So far, the prospects for new development look promising. The overall vacancy rate in the market did tick up to 17.3% in the first quarter, an increase of 30 bps, according to a new market study by Newmark Grubb Knight Frank. But that boost was largely due to the delivery of 150 North Riverside during the quarter, and 444 W. Lake St. in the previous one, which added 2.4 million square feet of space to the inventory.

But demand for such trophy spaces has been strong. In the first quarter, users absorbed another 544,000 square feet of class A space. And companies from a diverse cross-section of industries continue to see the CBD as a desirable location.

“The demand is stronger today than we've seen it in the last eight quarters,” Bob Chodos, vice chairman of NGKF, tells GlobeSt.com, especially when it comes to healthcare, tech and law firms. “It's exciting to see the number of tenants that are out looking for space.”

Bank of America , for example, plans to occupy about 500,000 square feet at 110 N. Wacker Dr., a proposed 51-story tower by Riverside Investment & Development and Howard Hughes that was recently approved by the Chicago Plan Commission . And many others have similar needs.

Researchers from NGKF recently found that, over the next few years, tenants needing a total of about 13 million square feet will test the Chicago market. “If I was a betting person, which I am, I would bet that in the next 18 months we will see another class A tower,” says Chodos.