(Bloomberg News) -- Eleven families promised to donate most of their wealth to philanthropy, joining the Giving Pledge initiative started by Warren Buffett and Bill and Melinda Gates.

Ninety-two families have now signed the pledge, according to an e-mailed statement from the initiative.

"This is a long-term effort, so it's exciting to see continued progress," Gates, the world's second-richest person according to the Bloomberg Billionaires Index, said in the statement. "This new group brings extensive business and philanthropic experience."

The families include Manoj Bhargava, Charles R. Bronfman, Dan and Jennifer Gilbert, Reed Hastings and Patty Quillin, Peter B. Lewis, Gordon and Betty Moore, Jonathan M. Nelson, Jorge M. and Darlene Perez, Claire and Leonard Tow, Albert Lee Ueltschi, and Dr. Romesh and Kathleen Wadhwani.

Buffett, 82, is the fourth-richest person on the planet with a net worth of $47.4 billion, according to Bloomberg's daily ranking. Gates, 56, has a fortune of $64.9 billion.