The rich keep getting richer.

Of the 94 colleges with endowments over $1 billion, 75 grew in market value last year, according to the just-released NACUBO-Commonfund Study of Endowments.

Harvard University added $565 million to its now $36.4 billion endowment. Put in perspective, that means Harvard’s endowment dwarfs the gross domestic product of nearly 100 foreign countries, based on 2014 data from the International Monetary Fund. (See the size of the endowment funds of the 10 wealthiest colleges in the table below.)

In all, 812 colleges participated in the study, and they reported an average one-year return on investments of 2.4% in fiscal year 2015, down from 15.5% in the year prior.

The report’s most troubling finding, according its authors, is that the endowments’ average long-term return is just 6.3%, significantly below the 7.5% 10-year target that most colleges aim for. That could have a lasting effect on how much colleges are able to spend, John Walda, president and CEO of the National Association of College and University Business Officers (NACUBO), said in a call with reporters Tuesday.

There’s a fairly direct relationship between endowment size and the one-year return rate, said William F. Jarvis, executive director of Commonfund Institute. Larger endowments performed better: Those with more than $1 billion had average returns of 4.3%, compared to roughly 2% for those funds with $100 million or less.

*Enrollment is the full-time equivalent based on enrollment data from the Integrated Postsecondary Education Data System
**$null: The University of Texas and Texas A&M University endowments encompass a system of multiple universities, not one campus like the others on the above list.