Despite 2016's shaky start, full of market volatility and some stock selloffs, office occupancy kept expanding over Q1 '16—albeit at a slower rate than most expansions. Here's a look at some of the powerhouses of the office REIT world, and how they're faring through the first bit of the year.

1. Boston Properties

Market Cap: $19.61B

Stock Price: $127.47

Founded: 1970

The biggest REIT on our list also happens to be the biggest office REIT in the US, with 46.5M rentable SF across 168 commercial properties. News broke last week that co-founder and chairman Mort Zuckerman (pictured) is set to step down next week, although he will remain in an honorary position and still be able to attend board meetings.

2. SL Green Realty

Market Cap: $9.59B

Stock Price: $96.08

Founded: 1980

SL Green's stock was upgraded by Goldman Sachs from "sell" to "neutral" yesterday, and the investment set a price target of $95, which the stock seems to be hovering right around. On the flip side, 16 brokerages rating the stock gave it a consensus price of $116/share for the year, so the REIT could grow its market cap very soon.

3. Alexandria Real Estate Equities

Market Cap: $6.64B

Stock Price: $90.86

Founded: 1994

In the 22 years since Jerry Sudarsky and Joel Marcus, founded Alexandria as a garage startup, the office REIT has blossomed into the third-biggest REIT in its sector. Alexandria focuses its investment particularly in properties of the life sciences industry.

4. Kilroy Realty

Market Cap: $5.70B

Stock Price: $61.53

Founded: 1996

The youngest REIT on this list, John Kilroy's (pictured) Kilroy Realty isn't just tearing it up on the stock market—the REIT also has an award-winning sustainability program.

5. Highwoods Properties

Market Cap: $4.56B

Stock Price: $47.48

Founded: 1978

Ed Fritsch's (pictured) Highwoods Properties rounds out the top five office REITs in terms of market cap—although Ed himself may not be quite as bullish on the REIT as investors are, as he just dumped 29,323 shares on March 18.