May 22 (Reuters) - Colombian President Juan Manuel Santos and right-wing economist Oscar Ivan Zuluaga go into Sunday's presidential election neck-and-neck in polls, meaning a second-round runoff in June is likely.
The main campaign issue has been peace talks with Marxist guerrillas that Santos launched in 2012 in hope of ending a 50-year civil war. Zuluaga says he is offering the rebels too much.
The following are the main candidates:
As defense minister for former President Alvaro Uribe, Santos led a successful campaign against the Revolutionary Armed Forces of Colombia (FARC) rebels. Santos and Uribe were allies but Santos broke with his former mentor after his 2010 election victory and later opened peace talks with FARC.
He won support with promises to end the war and help the economy, but the slow pace of the talks has made many impatient and spurred criticism that he is offering too many concessions.
A U.S.-trained economist, Santos warns the talks could collapse if he is not re-elected. Born into one of Colombia's most powerful families, Santos, 62, has followed market-friendly economic policies, helping to sustain solid growth.
Zuluaga has recently surged in the polls with promises to improve education and healthcare, and to defeat the rebels on the battlefield, a strategy championed by his mentor Uribe.
The 55-year-old, who served as finance minister under Uribe, says the government should not negotiate with the FARC while they are still at arms. He says he would support talks only if the FARC calls a unilateral ceasefire, and insists rebel leaders must serve prison time.
As finance minister, he was credited with bringing growth to Latin America's fourth-largest economy even as the global financial crisis battered other emerging markets.
He and Santos share the same basic economic policy ideas of developing natural resources and bringing in foreign investment.
A former mayor of Bogota, Penalosa, 59, is best known for improving its public transportation with rapid transit buses and expansion of bike paths during his 1999-2001 term.
Polling at around 10 percent as candidate of the center-left Green Alliance, Penalosa says he would continue peace talks if elected.
Ramirez, a lawyer and trade expert who also served as defense minister under Uribe, is polling in single digits, but her supporters could play a significant role in a runoff vote.
As defense minister, she changed the military's procurement system in an effort to curb corruption. The 59-year-old Conservative Party candidate says she would, if elected, give peace talks another four months before breaking them off.
Lopez, a Harvard-trained economist, has about 10 percent in polls as the candidate for the leftist Democratic Pole party.
A critic of the influence of right-wing paramilitary groups in government, she says she would seek a bilateral ceasefire to accompany peace negotiations. (Reporting by Julia Symmes Cobb and Helen Murphy; Editing by Kieran Murray and Chizu Nomiyama)