(CNN) -- Colombians will head to the polls Sunday to cast their votes in a runoff presidential election.
Former Defense Minister Juan Manuel Santos, who got 46.5 percent of the votes in the first round of elections in May, is leading in polls. A high-profile hostage rescue by Colombia's military gave another boost to his candidacy last week.
He is facing former Bogota Mayor Antanas Mockus, who received 21.5 percent of votes in the May election.
The winner of the runoff will replace Alvaro Uribe, a two-term president who has high approval ratings for his tough stand against Marxist guerrillas who have been waging war against the government since the 1960s.
