RIO DE JANEIRO, Aug. 20 (Xinhua) -- Although currently in jail, former Brazilian President Luiz Inacio Lula da Silva remains the leader of an election poll released on Monday.

It was the first poll conducted by the Brazilian Institute of Public Opinion and Statistics (IBOPE) after the Aug. 15 deadline for the registration of candidacies for Brazil's elections slated for October.

Lula's candidacy is still pending approval by the Superior Electoral Court, but IBOPE surveyed the scenarios both with and without Lula in the race.

In a scenario with Lula, the former president has 37 percent of voting intentions, while ultra-right-wing candidate Jair Bolsonaro, from the Social Liberal Party (PSL), is the runner-up, with 18 percent, followed by Marina Silva, from Rede, with 6 percent.

Sixteen percent of electors intend to register a null vote null and 6 percent remain undecided, according to the poll.

In a scenario without Lula, Bolsonaro takes the lead, with 20 percent of voting intentions, followed by Marina Silva, with 12 percent, and Ciro Gomes, from the Democratic Labor Party with 9 percent.

Fernando Haddad, who is currently Lula's running mate and would replace Lula as the Workers' Party's candidate if Lula is forbidden to run, currently has 4 percent of voting intentions.

In this scenario, the share of electors who said they will register a null vote reached 29 percent, and the undecided increased to 9 percent.

The scenario without Lula shows that a significant share of the former president's electors currently do not have a second choice of candidate, and, remarkably, a good share goes to Bolsonaro, who has a completely different political platform.

Other candidates like Ciro Gomes and Marina Silva also gain a share of Lula's votes.

The IBOPE poll was carried out among 2,002 electors from 142 towns all over Brazil on Aug. 17-19.

Lula, 72, has been found guilty of corruption and money-laundering in connection with the renovation of a beachside penthouse, which was bankrolled by a company seeking contracts with state oil giant Petrobras.

He is serving a 12-year jail sentence in Curitiba in southern Brazil.