Argentine oil and natural gas output hit a record high in May thanks to increased production from the country’s sprawling Vaca Muerta shale formation, the government said.

National gas production increased 7.6% in May compared with the same month last year, while oil production grew 4.2%.

“In May Argentina completed 13 straight months without needing to import crude oil, something that had not happened since 2012,” the energy’s secretariat said in a press release.

Vaca Muerta, a Belgium-sized shale formation in Neuquen province, is the key to Argentina’s plan for becoming a net energy exporter by 2020.

Vaca Muerta allowed the country to cut its energy deficit to $2.3 million in 2018 from $6.9 million in 2013. This year, the government hopes to erase the deficit and reach a surplus in 2020.