| Gustavo Petro (L) trailed Ivan Duque in the first round of voting |
Polls have opened in Colombia as voters decide which of two men will be their next president.
They have a stark choice between the business-friendly Ivan Duque, a newcomer to politics, and leftist ex-guerrilla Gustavo Petro.
The future of a historic but controversial peace deal with Farc Rebels hangs in the balance.
Corruption, the economy and inequality have all been big themes in campaigning for the run-off vote.
Polls close at 16:00 (21:00 GMT).
The two men in the running for the top job could not be more different, says the BBC's Katy Watson in Bogota.
Mr Duque, who is supported by a popular former president, the conservative Alvaro Uribe, comfortably won the first round last month and polls also give him the lead this time.
The orthodox economist says he will rewrite the 2016 agreement which gave Farc Rebels an entitlement to representation in Congress, and will revisit crimes allegedly committed by the rebels during the brutal long-running conflict.
For his part, Mr Petro says he wants to tackle social inequality, redistribute land and end Colombia's reliance on extractive industries in favour of renewable energy.
Source: BBCNews
