When it comes to self-made billionaires, America leads the world.

Six of the world’s top 10 self-made billionaires are American, according to private wealth consultancy Wealth-X. Their complete list of the top 25 self-made billionaires features many notable Americans, including the founders of holding company Berkshire Hathaway Inc. BRK.A, -3.57% and computer technology company Oracle Corp. ORCL, +1.14% , but the list doesn’t include any women. The combined wealth of the 14 Americans on the Wealth-X list is $514.2 billion, which is greater than the gross domestic product of Norway. (Google Inc. co-founders Larry Page and Sergey Brin were No. 11 and 12 on the list.)