The old adage that everything is bigger in America certainly rings true this year. Forbes' list of the richest Americans reveals some astounding fortunes - including the richest man in the world, and a man who added $12.5 billion to his wealth in just one year.
So who are the top ten richest Americans, and how have they made their fortunes?
Forbes has published its top 400 of the richest billionaires in the US.
1. Bill Gates $72 billionThe co-founder of Microsoft takes the title as richest American for the 20th year running - and re-takes the title of richest man in the world from Mexico's Carlos Slim. This is despite the fact that he has given away $28 billion - most of it to the Bill & Melinda Gates Foundation. Microsoft now makes up under a fifth of his fortune, as his investment company has made a number of major investments.
2. Warren Buffett $58.5 billionThe investment mogul didn't let his age of 83 slow him down in his pursuit of more wealth last year - making $12.5 billion - more than anyone else on the list. He also acquired Heinz during the year. His huge wealth is despite the fact that during his lifetime he has given away $20 billion to the Gates Foundation.
3. Larry Ellison $41 billionThe founder of Oracle is 69, but it hasn't slowed his ambitions for the company, his America's Cup team or his property collection. He is also working on reversing the effects of age - and has donated $445 million to his own medical foundation which does research into ageing and age-related diseases.
4. Charles Koch $36 billionThe CEO of Koch Industries - the second biggest company in America - isn't taking it any easier now he has hit the age of 77. The company continues to expand - taking his wealth with it. He is $5 billion richer than this time last year.
5. David Koch $36 billionThe second beneficiary from the success of Koch Industries. The Executive Vice President is also the richest man in New York, and like his brother he saw his wealth rise $5 billion last year. Both brothers invest 90% of everything they earn into the business.
6. Christy Walton $35.4 billionThe richest woman in America owes her fortune to the success of Wal-Mart - founded by her father-in-law Sam Walton and his brother in 1962. Christy inherited her wealth when her husband died in a plane crash in 2005.
7. Jim Walton $33.8 billionAnother Wal-Mart beneficiary (and the youngest son of Sam). He is also CEO of the family bank - which had profits of almost $100 million in 2012.
8. Alice Walton $33.5 millionSam's daughter runs a horse ranch in Texas, and founded the Crystal Bridges Museum of American Art in 2011. She is also the most generous philanthropist of the family.
9. Rob Walton $33.3 billionThe chairman of Wal-Mart stores is the oldest son of Sam Walton at the age of 69.
10. Michael Bloomberg $31 billionThe Mayor of New York and founder of the financial data company that made his fortune in 1982 (after he was fired from Soloman Brothers). He is set to leave his post next year, and there has been speculation as to whether he has further political ambitions. He has given away $2.8 billion of his fortune in his lifetime.
The rest of the top 20 were made up of Sheldon Adelson the Vegas casino billionaire, Amazon's Jeff Bezos, Google's Larry Page and Sergey Brin, Mars dynasty beneficiaries Forrest Mars, Jacqueline Mars and John Mars, investment gurus Carl Icahn and George Soros, and Facebook's Mark Zuckerberg.
Notable mentions are due to Mark Zuckerberg, who made it back into the top 20 on the back of strong stockmarket performance by Facebook. Meanwhile, the highest new self-made entrant to the top 400 was John Morris, the founder of Bass Pro sporting goods shops, who is worth $4 billion.
Bill Gates is the only member of the top 10 under the age of 60 (excluding those who inherited their wealth), while at 29 Zuckerberg is the only member of the top 20 under the age of 30.