He would not name the oil companies, for his own security.
Companies operating or exploring in Meta and Guaviare include Canadian-owned Pacific Rubiales, Exxon Mobil Corp., Brazilian-owned Petrobras, and Petrominerales â¿¿ a Colombian affiliate of Canadian-owned Petrobank.
"Part of the reason why Colombia, unlike many of its neighbors, was forced to provide so many tax incentives and regulatory sweeteners was precisely because they had to deal with that legacy of insecurity," Esteruelas said.
Those incentives helped persuade Pacific Rubiales to begin investing in Colombia in 2004, said the company's vice president, Jose Francisco Arata.
Colombia's second-largest oil company after Ecopetrol, Pacific Rubiales moved into formerly rebel-held areas of Meta and its production is now up to 125,000 barrels a day.
Over the next year, the company plans to invest $235 million in further exploration in the eastern plains, as well as in the lowlands of the southern state of Putumayo â¿¿ both areas of continued rebel activity.
"In areas that are considered a high risk, like in the border regions with Venezuela and Ecuador, military forces will accompany oil operators," said Armando Zamora, regulator for the National Agency of Hydrocarbons.
Just last year, he said, the Revolutionary Armed Forces of Colombia, or FARC, burned some trucks and tried intimidating workers during an oil operation in the southern state of Putumayo, which borders Ecuador. He wouldn't detail the incident.
To Rodriguez, the former environmental minister, the intimidation, violence and extortion are simply the price of doing business in Colombia.
After all, he said, major coal operations began in Colombia during the peak of its conflict.
"Historically, the country's violence hasn't been the biggest difficulty for outside companies," Avila said. "The biggest difficulty was that they didn't know the region. And now that they've done preliminary studies and know, they're investing more."