Oxfam forgot to mention  this:

"Created by Berkshire Hathaway CEO Warren Buffett and Bill and Melinda Gates, the Giving Pledge invites the wealthiest people in the world to pledge more than half of their wealth to charitable causes either during their lives or in their wills. As of June, 137 ultra-wealthy individuals and families have joined the effort, with some pledging to allocate more than 99% of their money to philanthropy."