A worldwide economic boom has yielded a record number of dollar billionaires in the past year, according to Forbes. Their number rose by 15%. Microsoft's Bill Gates tops the list for the 12th year running, with a net worth of $50bn (29bn). The combined net worth of the 793 is $2.6 trillion and US billionaires account for just under half the amount. The figures were conservative estimates for different reasons. While New York has the highest number of resident billionaires with 40, Moscow is second with 25, and London comes third with 23. Steve Forbes, Forbes' chief executive and editor-in-chief, attributed the global rise in the number of billionaires to an economic boom.