It took gifts totaling at least $37.5 million to make the list this year. Forty-two of the top 50 made gifts of $50 million or more.
Thirty made big gifts to colleges and universities, but Palmer noted most college gifts went to science and research this year, not to buildings, as in previous years.
Ten of the 50 made the list because of bequests after their deaths, including the second biggest giver in 2013, George Mitchell, a Galveston, Texas, man who made his fortune in energy and real estate.
At No. 3 were Nike chairman Philip Knight and his wife, Penelope, of Portland, Ore., who made a $500 million challenge grant to Oregon Health & Science University Foundation for cancer research. The Knight pledge requires the university match it within the next two years.
No. 4 was philanthropist and former New York mayor Michael Bloomberg, who made gifts totaling $452 million in 2013 to arts, education, environment, public health and other causes.
Nineteen people or couples on the list have signed the Giving Pledge, started by Bill Gates and Warren Buffett in 2010. More than 120 of the world's wealthiest individuals and families have pledged to give at least half their wealth to charity since the movement began.
Although most people on the list were prominent wealthy people who have given generously in the past, Palmer said a few were surprises, including Jack MacDonald, a Seattle lawyer, who gave $139 million to three nonprofits upon his death.
