One-hundred and thirty-eight companies from 21 countries, some of which already operate in the Andean country, attended the auction launch, Ecopetrol said in a statement.
"The fields are close to logistical facilities, which adds extra attraction for small and medium sized gas and oil companies," the company said.
The blocks will be sold in an electronic auction 30 September.
Ecopetrol has been selling assets in a bid to fund its investment plan, which is down by $1.8
