Echoing Venezuelans' top concerns, the five candidates have all stressed reducing crime and cutting unemployment as their priorities in the South American OPEC nation.
Following are details of the candidates:
HENRIQUE CAPRILES
The youthful governor of Miranda state leads polls ahead of the opposition Democratic Unity coalition's primary.
Charismatic and energetic, the 39-year-old Capriles rides a motorbike and heads into shantytowns most days to supervise projects and talk to working-class voters.
A keen basketball player and sports lover, he was the country's youngest legislator at 26 and defeated a powerful Chavez ally to win the Miranda governorship in 2008.
He was jailed for four months on charges of fomenting a protest at the Cuban Embassy in 2002, although he said he was mediating. He was acquitted of the charges at trial.
If elected, Capriles wants to copy Brazil's "modern left" model of economic and social policies. On the campaign trail, he has sought to appeal to traditional Chavez supporters, stressing inclusiveness rather than attacking the president, and urging Venezuelans to "get on the bus" for change.
"God willing, I will be the youngest president in Venezuela's history," he has said.
PABLO PEREZ
Another prominent figure of the opposition's "youth wing" is Pablo Perez, 42, governor of the oil-producing western state of Zulia. He is running second to Capriles in the polls and is trying to project himself as the candidate who has the most in common with Venezuela's poor majority.
Perez has the important endorsement of two heavyweight parties from the pre-Chavez era: Democratic Action and Copei. While he may benefit from their formidable nationwide political machinery, the parties' history of corruption and nepotism could work against him.
The center-left politician is a lawyer by training and also a lover of sport, especially basketball.
State TV has run a campaign against him, including showing murky footage of an incident where he was allegedly drunk and aggressive. Supporters say the images were manipulated.
Perez has governed Zulia and its 4 million people since 2008. The oldest of five brothers and father of three, he comes from Maracaibo, Venezuela's second city, whose people often boast of their "independence" from the rest of the nation.
"Our only enemies are unemployment, impunity, insecurity, high living costs, corruption and poverty," he said. "I will be the big father of the Venezuelan family."
MARIA CORINA MACHADO
Though trailing in the polls, the fiery right-winger has been widely praised for debate performances where she reeled off more data and details than her rivals.
Machado, 43, also shot to national prominence after sparring bitterly with Chavez during a parliamentary session last month.
Suggesting his much-vaunted nationalizations were tantamount to theft, Machado drew some withering put-downs from Chavez and his allies have turned on her since then.
Recently elected as a legislator, she is an industrial engineer by training and is popular among the well-to-do in Caracas but hated by many Chavez supporters, in part because of a photo showing her warmly greeting former U.S. President George W. Bush.
Machado's campaign gained more attention when several gunshots were fired close to her group during a visit to a Caracas slum that is a pro-Chavez stronghold. She blamed criminals and said she would return there.
Police were furious at her assertion in one debate that 12,000 small drug trafficking gangs exist in Venezuela.
DIEGO ARRIA
Generally considered an outsider for the opposition presidential ticket, Arria, 73, nevertheless impressed viewers with deeper, different and more historically nuanced answers to most of the questions in a string of debates.
A former governor, minister and envoy to the United Nations in the early 1990s, Arria appears to be positioning himself as something of an elder statesman for the opposition movement.
Having had his ranch seized by the government in a dispute over title deeds, Arria has a major bone to pick with Chavez and is the most outspoken in his criticism of the president. He has said Chavez should face an international court.
PABLO MEDINA
A rank outsider in the primary race, Pablo Medina, 64, was a
conspirator with Chavez during his failed 1992 coup attempt against then President Carlos Andres Perez.
Eight years later, Medina turned against Chavez in what the president's supporters call a "betrayal" they will not forget.
The former steel worker, union leader, guerrilla and legislator was one of the founders in the 1970s of the Marxist-leaning Radical Cause party that backed Chavez's successful presidential campaign in 1998.
(Reporting by Diego Ore and Andrew Cawthorne; Editing by Kieran Murray and Christopher Wilson)
