Ekvall fears that phantom votes could be stuffed into ballots in places where witnesses from the opposition do not have a strong presence. In this election, however, witnesses from Venezuela's opposition will cover a far greater amount of voting booths than in the 2006 presidential election, he said.
According to Ekvall, Capriles' chances of winning could also be hampered by the perception amongst many Venezuelan voters that the government "can tell who they're voting for."
Ekvall explained that in Venezuelan voting booths, a machine that takes your fingerprint and then shows you your photo on a screen is linked by a cable to another machine with a touch screen, on which you actually cast your vote.
He believes that this set up has stoked fears amongst voters that the government can identify who voted for which candidate. "Many people will not want to risk voting for the opposition and losing benefits," Ekvall said.
Ekvall pointed out that in a survey conducted by local pollster Alfredo Keller in early September, 21 percent of Venezuelans said they thought the government could tell who they would vote for. Another 21 percent refused to answer the question.
Manuel Malaver writes a political column on the Venezuelan news portal noticias21. He's also a consultant for international media outlets.
"I think Capriles has a moderate chance of winning," Malaver said. "I get a lot of information from local newspaper journalists across Venezuela, and based on this, I would say that polls are underestimating how many votes Capriles can get."
Malaver predicted a 4 to 6 point victory for Capriles, even though some polls in Venezuela gave Chávez a lead of 10 points or more in the last week of September.
"Two important things have happened in this campaign," Malaver said, citing Chávez's well publicized fight with cancer. "First of all, Chávez's mobility has been very limited due to his illness. Capriles has mobilized the country in a way that has not been seen here in decades. He's generated an emotional connection with people, especially with youth."
Malaver mentioned that in order to make up for his lack of mobility, Chávez made frequent use of a law that allows the president of Venezuela to take over the airwaves to deliver messages that are "of national interest." The TV appearances averaged 30 minutes a day during the campaign.
"The overwhelming presence of these broadcasts also shows that there is some fear on behalf of the government that they could lose the election," Malaver said.
Would Chavez accept defeat?
"Taking into account that he dominates institutions like the national electoral council, he might feel tempted to pull some moves that would lead him not to recognize results, but only if Capriles does not win by a wide margin." Malaver said.
"But signals are mixed. We have avoided crossing the red line that would lead to a civil war over the past 14 years, despite the country's [political] polarization. Chavismo is weakened as well, so I think the chances that he would accept [defeat] are high," said Malaver, who also said that in the past Chavez had accepted defeats in less important electoral races.
Cynthia Arnson directs the Latin America program at the Woodrow Wilson International Center for Scholars. She declined to make a prediction on Sunday's vote.