Chavez has said no one can question the fairness of the country's electoral system, and that his government's spending is aimed at promoting the country's development and addressing the needs of Venezuelans.
About 16 percent of registered voters cast ballots in the primary, far surpassing the opposition's goal of 10 percent to 12 percent.
Venezuelan pollster Luis Vicente Leon called the turnout historic, both for the opposition and for the country. He said previous primaries by Chavez's party haven't drawn so many voters.
Venezuela has grown heavily polarized, with most either admiring or despising Chavez. About one-fourth of voters are in neither political camp, though, and in that group about 10 to 15 percent are likely to cast ballots, Leon said. Many of the swing voters are young people who have grown up during Chavez's presidency, Leon said.
In order to compete, Capriles will likely need to win over voters who leaned pro-Chavez in the past, who have grown disillusioned with the government and don't strongly identify with either side.
Adam Isacson, an analyst at the Washington Office on Latin America, said the opposition seems to be on solid footing.
"They have a charismatic, credible candidate who â¿¿ since he has spent most of his adult life in Chavez's Venezuela â¿¿ doesn't carry the baggage of the corrupt governments that came before Hugo Chavez," Isacson said. "And the opposition no doubt benefits from a bout of 'Chavez fatigue' in Venezuela: even many voters who think fondly of Hugo Chavez may feel that 14 years is enough, and his cancer has made many start to envision a post-Chavez Venezuela for the first time in a while."
Chavez's approval ratings have topped 50 percent in recent polls, and his struggle with cancer doesn't appear to have hurt his popularity. The 57-year-old president says he's cancer-free after undergoing surgery and chemotherapy last year, and has been energetic in his hours-long television appearances, apparently trying to show he can still keep up with a younger challenger.