Latin America's three most populous nations – Brazil, Mexico and Colombia – are having scheduled presidential elections this year. Venezuela, which has the sixth largest population, is having a snap vote. Here is a snapshot of the contests.

Right-wing candidate Ivan Duque and leftist Gustavo Petro are the leading contenders at the head of their respective coalitions in Colombia’s presidential elections on May 27. 

An opinion survey late last month gave Duque, 41, of the Democratic Center party a comfortable lead, with 37 percent of Colombian electors saying they plan to support him in the latest poll. He is also the candidate with the most favorable image (49 percent) among voters.

Petro, a 57-year-old former M-19 fighter and previous mayor of Bogota who heads the left-wing coalition, was in second place with 29 percent; centrist Sergio Fajardo, a former mayor of Medellin, third with 15 percent and the center-right German Vargas Lleras, an ex-vice president, at eight percent.

Duque, a lawyer and senator who worked at the United Nations, has pledged to promote social and economic reforms.

Supporters of 57-year-old Petro’s Colombia Humana party highlight his work to improve conditions for the poor. He has pledged to create a “social economy” that will shift the economy from oil toward agriculture. He is seen by the private sector as less business-friendly than his opponent.

Of significance is that Duque, who was handpicked by former president Alvaro Uribe, opposes the peace deal between the Colombian government and FARC fighters, and may seek fundamental changes to the agreement if he wins. He should be encouraged as supporters of peace parties lost seats in legislative elections in March when the Democratic party formed the largest bloc in the Senate.

FARC, which has been transformed into a political group, also flopped and its leader, Rodrigo Londono, has since dropped out of the presidential election on health grounds.

Whoever wins will inherit an extended list of things to do, including matters linked to the implementation of the peace accord. But surveys indicate that people have other pressing concerns such as corruption, education, the state of the economy, health and security.

If no candidate receives a majority of the vote in round one, a second round will be held on June 17.

In Mexico, where presidential and legislative elections will be held on July 1, a left-wing candidate has led the most recent opinion polls. A survey of 1,200 voters by polling firm BGC published on Monday put Lopez Obrador's support at 42 percent. His closest rival Ricardo Anaya, who heads a right-left coalition, has 33 percent, and Jose Antonio Meade of the ruling Institutional Revolutionary Party (PRI), 19 percent.

A one-time mayor of Mexico City, Lopez Obrador of the National Regeneration Movement (Morena) will be running for the third time. He came second in the two previous presidential elections and has led in opinion polls for months. Given Mexico’s first-past-the-post system in a single round of voting, he could well prevail.

The bid by 64-year-old Lopez Obrador, whose nickname is Amlo, has capitalized on deep-seated discontent with the PRI over rising gang violence, corruption scandals and sluggish economic growth. Some analysts also say the result will determine whether voters want to see a more robust response by Mexico to US President Donald Trump's harsh rhetoric towards America's southern neighbor. Trump’s bad experiences investing in Mexico were the reason for his negative view of the country, Lopez Obrador has said, and he plans to change that perception by ending corruption in the Central American nation.

The poll also showed that Obrador's party is backed by 39 percent of Mexicans in voting for the lower house of Congress with allies predicted to win another five percent between them. Support for Anaya’s center-right National Action Party (PAN) stood at 25 percent, with its two coalition partners having another 10 percent support.

The PRI, which until 2000 held a 70-year grip on government before making a comeback in 2012, attracted 18 percent of the vote in the lower house, with two allies together mustering another three percent.

He may be the favorite, but Lopez Obrador has some serious detractors. "The prospect of a six-year presidency by Amlo horrifies his many detractors and foes who paint him as an Hugo Chavez-style authoritarian and 'tropical messiah' whose antiquated policies would ruin the Mexican economy," The Guardian said in a report on Tuesday. But the paper said he has sought to assuage those concerns by promising business leaders, who he has in the past branded as corrupt, that there will be “no expropriations, no nationalizations” if he wins.

Formal campaigning for Brazil's presidential election in October doesn't begin until August. But so-called pre-campaigning has been clouded by the jailing of former president Luiz Inacio Lula da Silva for corruption last month.

The election is taking place as the so-called Car Wash, Brazil’s biggest investigation into political corruption, enters its fifth year. Lula is a victim of the probe which has also implicated many members of the legislature.

As a result of the scandal, candidates have been barred from using donations from corporations while the period of official campaigning has been slashed. The political turmoil, as well as a deep economic recession, have angered voters across the country.

Before his conviction, Lula was the leading presidential candidate, according to opinion polls, and his withdrawal – unless he is able to overturn his 12-year sentence – has made the race wide open.  

If Lula's Workers' Party decides to choose a successor, the likely replacement is former Bahia governor Jaques Wagner. Without Lula, an opinion poll conducted a week after he began his sentence suggested that environmentalist Marina Silva, who broke with the Workers' Party, and right-wing politician Jair Bolsonaro are the leading candidates.

Some analysts say Bolsonar, who presented himself as the anti-Lula candidate and dispenses harsh rhetoric against the left, corruption and homosexuality, could lose some of his luster now that Lula appears to be out of the race.

Other possible contenders may include current President Michel Temer, though he has dismally low approval ratings; center-right former Sao Paulo governor Geraldo Alckmin, the city's former mayor Joao Doria, Joaquim Barbosa, a black former Supreme Court president; TV presenter Luciano Huck and finance minister Henrique Meirelles. 

Venezuela is due to hold a snap election on May 20.

President Nicolas Maduro will run for a second six-year term. His nearest opposition rival is Henri Falcon, 56, a former soldier and state governor, while the two most popular opposition figures, Leopoldo Lopez and Capriles, have both been banned from standing. Lopez is under house arrest accused of fomenting violence in anti-Maduro demonstrations in 2014, while Capriles is prohibited from holding office on a charge of “administrative irregularities” when he was a state governor. Both men say the accusations were made up to sideline them.

The election is taking place against the background of a prolonged economic and political crisis which has distressed many Venezuelans and led hundreds of thousands to flee the country.

The US and the European Union say the vote will be neither free nor fair, but Maduro says he doesn't care what they think. He has claimed in the past that the US had sabotaged the Venezuelan economy, but Washington cites alleged mismanagement and corruption.  

In a speech at the Organization of American States on Monday, American Vice President Mike Pence called for the suspension of the election, saying it was "no more than fraud and sham." Samuel Moncada, Venezuela's deputy foreign relations minister for North America, called Pence remarks a "farce" and a "monstrosity."

Campaigning has been described as lackluster, as many people in the country are preoccupied with seeking out the necessities of life, like food and medicine.

Maduro still commands support from his hardcore base. “Things are tough, you can’t deny it. He has made many mistakes. But I will still be voting for Maduro because he is the legacy of (late president Hugo) Chavez,” said welder Johan Quintero.