Colombia's state oil company Ecopetrol offered 20 oil and gas blocks for auction on June 23, part of a company plan to cut back amid low global crude prices. The blocks will be sold in an electronic auction on Sept. 30.

Ecopetrol said in a statement that 138 companies from 21 countries, some of which already operate in Colombia, attended the auction launch.

"The fields are close to logistical facilities, which adds extra attraction for small- and medium-sized gas and oil companies," the company said.

Ecopetrol has been selling assets in a bid to fund its investment plan, which is down by $1.8 billion this year.