For the second year in a row, Mexican telecom tycoon Carlos Slim Helu takes the title of world’s richest man on Forbes’ annual World Billionaires’ list, with a record-breaking fortune of $74 billion. His net worth grew $20.5 billion in a year.

Several factors drove the increase. The Mexican stock market has been on a tear over the past year, rising 19% (in peso terms), and the peso has strengthened 7% against the dollar. Some 62% of Slim’s fortune, which he shares with his children, lies in his controlling stake in Latin American wireless phone company America Movil. Its shares rose 18% over the past year.

Nearly $10 billion in gains came from two successful spinoffs from Slim’s Grupo Carso conglomerate. In January,  Carso spun off Mineras Frisco, a mining play now worth $7.9 billion to Slim; and Inmuebles Carso, a real estate investment company that added $1.95 billion to his net worth. Both trade on the Mexican stock market. (All of this figuring was done using stock prices and exchange rates from February 14, 2011, and comparing them to prices we used for the 2010 World’s Billionaires list from February 12, 2010.)

Not bad for a year’s work.

Bill Gates and Warren Buffett have not yet convinced Slim to join their Giving Pledge, a promise that close to 60 of the super wealthy  (including Facebook’s Mark Zuckerberg and Facebook cofounder Dustin Moskovitz) have made to give away half their wealth during their lifetimes or after they die. I’ll write more soon about Slim’s philanthropic activity, but one recent move is that the stunning new Mexico City museum housing Slim’s vast art collection, Museo Soumaya, will be open to the public for free.