#2. George Kaiser: $4 Billion (current total Net Worth $10 Billion)
One of the top 100 richest people in the world, George Kaiser inherited Kaiser-Francis Oil Co. from his uncle and parents in 1969. In 1990 he bought the Bank of Oklahoma, putting him on Forbes list of 400 wealthiest Americans.
Through the George Kaiser Family Foundation, Kaiser has funded efforts to fight child poverty, develop alternative sources of energy, and combat drugs and poverty throughout his native city of Tulsa. Source