What is happening with Venezuela's election?

Gonzalez leads by 20 points in polls, but concerns about election fairness persist among opposition and observers.

Venezuelans are preparing to vote in a presidential contest this Sunday that pits incumbent President Nicolas Maduro against opposition candidate Edmundo Gonzalez.

Gonzalez has been leading in opinion polls by some 20 points, but the opposition and some observers have questioned whether the vote will be fair.

When is the Election?

The presidential election is set to take place on July 28. It is a simple majority-wins vote.

The opposition boycotted the 2018 contest, saying conditions for a fair vote did not exist.

Maduro, a former bus driver who was the hand-picked successor of his mentor Hugo Chavez, has been in power since Chavez's death in 2013 and is seeking his third six-year term.

His government has presided over a sharp economic and social deterioration. The US reimposed oil sanctions in April, accusing Maduro of reneging on deals reached with the opposition to ensure free elections.

Who is the Opposition Candidate?

A long-time but low-profile member of the opposition, Gonzalez, 74, a former diplomat, is known for his calm demeanor.

He was originally registered as a placeholder in March, after neither opposition primary winner Maria Corina Machado nor her alternate were able to register. In April, he was named as the opposition's definitive candidate.

Machado, 56, has thrown herself into campaigning for Gonzalez. The two - speaking to large crowds around the country - have employed emotional rhetoric, including about their hope for the many who have emigrated from Venezuela in recent years to return home.

What have Maduro and Gonzalez each Promised?

Maduro, whose face will appear on the ballot for 13 parties, says he will guarantee peace and economic growth that will make Venezuela less dependent on oil income.

Maduro, 61, has always denied accusations that he is authoritarian and has spent much of his campaign inaugurating social infrastructure like schools and clinics.

Gonzalez has said he is committed to carrying out a transition that will allow exiled people to return to the country and political prisoners to be freed.

When Machado was campaigning on her own behalf, she expressed support for privatizing state-owned energy behemoth PDVSA and other public companies, in addition to building a welfare program to help the poorest.

Who Else is Running?

Nine other candidates, who each have minimal support, are also on the ballot. Many are seen as government supporters by the opposition.

When are the Results?

Campaigning officially closes on Thursday, before voting on Sunday. Results could be published that same evening or in the following days.

Will the Election be Free?

That remains to be seen. Some in the opposition fear Gonzalez's place on the ballot could still be withdrawn or that he could face a public office ban.

Though Maduro has said the country has the world's most transparent electoral system, the opposition and analysts say decisions by electoral authorities – from polling station staffing to the lay-out of the ballot – were made with the intention of confusing voters and creating obstacles to a free vote.

The opposition has also decried the detentions of some of its staff and allies, including the arrest and then release of Machado's head of security last week.