Mexico City - Mexican tycoon Carlos Slim held the title of the world's richest man for the past three years until a new president rolled into town with a vast economic reform agenda.

Enrique Pena Nieto's push to overhaul the telecoms industry, a sector dominated by Slim, has weighed down on stock prices of the billionaire's America Movil phone empire, analysts say.

Three weeks after Congress approved the legislation, and a boatload of dollars later, Forbes magazine declared Wednesday that Microsoft founder Bill Gates had reclaimed the wealth throne he bequeathed to Slim in 2010.

Slim's US$69.1 billion compared to US$69.8 billion for Gates after America Movil shares dropped further - a spectacular reversal of fortune from just over a month ago, when Forbes put Slim on top of its 2013 rich list with a net worth of US$73 billion.

Jorge Bravo, web editor of the industry consultancy Mediatelecom, said reaching the top of the list had ultimately backfired on Slim.

"A series of regulations and media effects began against him for being the richest man in the world in a country that doesn't exactly have his wealth and has a lot of poverty," Bravo told AFP.

"I have no doubt it was the worst event that could have happened to him," he said, voicing doubts on whether Slim should have overtaken Gates at all.

"You can't compare a company that is very profitable and has a continental presence in Latin America with Microsoft, which is global," he said.

Slim's spokesman declined to comment.

America Movil owns fixed-line and mobile phone businesses as well as Internet and cable television services in 17 Latin American nations and the United States.

In Mexico, his landline firm Telmex controls 80 per cent of the industry while his cellphone service, Telcel, holds 70 per cent of the mobile market.

Pena Nieto took office in December with a pledge to reform key sectors in the country, forming an unprecedented pact with rivals to lock down support.

The telecoms bill has yet to become law and the impact it will have on Slim's dominion remains unclear, analysts said, but it has made investors shy away from America Movil.

The company's shares closed at 12.54 pesos (US$1) on the Mexico stock exchange on Friday, down 0.32 per cent from the previous day.

"The concern is that the government wants to reduce his dominance with the idea of having more competition in the sector with lower prices," said Carlos Hermosillo, an analyst at Banorte bank.

Ignacio Cedillo Bravo, an analyst with financial consultancy Bursametrica, said Slim's other companies - with interests in mining, auto parts and retail - have also been affected by a general drop in Mexico's stock market, which has fallen 7.29 per cent over the past year.

While the reforms have hurt America Movil's shares, Slim could reclaim his title if the stock market rebounds.

The telecoms bill aims to open up competition in the telephone and television market, which is dominated by Televisa, the world's biggest Spanish-language broadcaster.

The legislation creates two new autonomous regulators and seeks to increase outside investments in the market, allowing foreign companies to own 100 per cent of the capital of a phone firm and almost half of radio and television broadcasters.

Although Slim has tried to break into the television market, Mediatelecom's Bravo said the reform may not help him because it will have very short deadlines to open new TV stations.

But he said another reform eyed by Pena Nieto could help the 73-year-old billionaire further diversify his portfolio: An overhaul of the energy sector which could allow more private investment in the state-run Pemex oil giant.

"Among national businessmen who could participate in the energy sector in case the Pena Nieto government decides to open it up, he would without a doubt be one of the main Mexican candidates," he said.