(Fortune Magazine) -- In the hills above Mexico City, well-to-do supporters of presidential candidate Felipe Calderón hand the keys of gleaming late-model cars to parking attendants, then listen approvingly as he calls for sending kidnappers to prison for life.

In the center of the city, with its crooked pavement and decaying buildings, another candidate, Andrés Manuel López Obrador, jumps out of a black SUV into an enthusiastic crowd waiting for the premiere of a film portraying him as an activist for social justice.

In the weeks leading up to Mexico's July 2 election, the two main candidates - one a pro-business ally of outgoing President Vicente Fox, the other a populist left-wing former mayor of Mexico City - hurled allegations of corruption and staked out sharply different positions. But regardless of who wins, one outcome is all but certain: Mexico's oligarchs will remain on top.

A quarter-century of corruption, misadministration, and economic stagnation has led to a loss of government credibility in this country of 100 million people. Large business interests - often oligopolies with dominant market shares in basic goods like telephones, cement, beer, corn flour, and television - at times seem to eclipse the government itself.

Rescue packages for troubled companies and poorly administered privatizations have left many with a simmering sense of injustice. Even a veteran of previous regimes, senator and former secretary of state Manuel Bartlett, a member of the PRI Party that ruled Mexico for 71 years before being ousted by Fox, acknowledges as much. "At this moment in time," Bartlett says, "Mexico is a plutocracy."

That's nothing new. Mexico has long been in the grip of oligarchs like Emilio Azcárraga, whose family owns media giant Televisa, which commands about 70% of the country's television audience - and not inconsiderable political clout. Or Lorenzo Zambrano, who runs Cemex, which produces about 60% of the cement in Mexico. Or Maria Asunción Aramburuzabala, vice chairman of Grupo Modelo, which controls more than 60% of the Mexican beer market.

And then there's Carlos Slim, a self-made billionaire, Mexico's richest and most powerful citizen, who made his $30 billion fortune through ownership of telephone monopoly Telmex, which has an estimated 95% share of Mexico's domestic fixed-line business. Companies Slim controls account for more than 45% of the capitalization of the Mexican stock exchange.

López Obrador would seem a natural enemy of this crowd. He has been critical of Roberto Hernández, a billionaire board member of Citigroup, who built his fortune in the 1990s by buying Mexico's largest bank, Banamex, during a privatization, then selling it to Citigroup. And the candidate has come out against privatization of Mexico's troubled state-owned oil company, Pemex.

But don't expect a showdown with Mexico's oligarchs if López Obrador wins. "The solution is not going to war [with big business], because then we would provoke chaos in the country," says Manuel Camacho Solís, López Obrador's chief campaign strategist and a former foreign affairs minister. "But we need to recover the capacity for independent regulation, which isn't submitted to special interests."

López Obrador has proved he can work with the country's big wheels. When he was mayor, he collaborated with Slim in a project to restore the city center. And although he has an independent streak, López Obrador might be seen as a friend of big business when infrastructure projects like the long, winding overpasses he built in Mexico City start bringing money into the coffers of companies like Slim's Condumex and Zambrano's Cemex. The oligarchs have also learned that a little left-of-center protectionism never hurt their interests.

For the most part Mexico's business elite has stayed above the political fray. But last fall Slim put forward a reform program calling for sounder public finances; investment in health, education, and public security; fuller employment; and economic development.

The document was notable for the absence of the word "competition," which didn't stop more than half of the country's governors, as well as Calderón and Roberto Madrazo, the candidate of the PRI, from signing it. López Obrador said he would sign only if clauses were added against corruption and the privatization of Pemex, which didn't happen.

"This document is basically an appeal to maintain the status quo," says Javier Corral, a senator in Calderón's Partido de Acción Nacional, or PAN. "It shows how powerful he is that he can pass the pen around and have governors and even presidential candidates sign his policy platform."

Slim isn't the only oligarch who has made political waves. Earlier this year Televisa lobbied a suppliant congress to pass a media law creating bidding procedures favorable to the television oligopoly in the allocation of new spectrum. None of the presidential candidates opposed the law.

"The head of the PRI in the senate told me that if we wanted Madrazo to lose, we should oppose the Televisa law," says Bartlett, who has since switched his allegiance to López Obrador.

Televisa's board is a Who's Who of Mexican business and counts four billionaires among its members, including Azcárraga, Banamex's Hernández, Grupo Modelo's Aramburuzabala, and Alberto Bailleres, who owns the world's richest silver mine.

"The board of Televisa is a transversal power reaching many dimensions of the economic and political life of the country," says PAN senator Corral. "It has the power to impose its own agenda on the constitutional powers of the country."

Beyond campaign funding and other levers that come with great wealth, Mexico's oligarchs have a not-so-secret weapon: the threat to move their money out of the country, as they did on the eve of the peso devaluation in 1994. This means that any serious attempt to break the oligopolies could result in economic crisis.

But while companies run by oligarchs may be efficient, they often charge higher prices - it costs about three times as much to call the U.S. from Mexico City as the other way around - and not to introduce more competition is to doom the country to further stagnation. That's the challenge for the winner, who will take over a country that is two parts oligarchy and one part anarchy, and where the President governs none of it.