Repsol SA discovered 4 trillion cubic feet (Tcf) of possible natural gas reserves in Bolivia that it will start tapping in 2019, the government and company said Feb. 19—a finding that could boost the Andean country's reserves by 40%.

The three new fields—Boicobo, Ipaguazu and Boyuy—in the Caipipendi block in southern Bolivia contain enough gas to meet the demands of neighboring Brazil over 10 years, said Diego Diaz, the head of Repsol's Bolivian unit.

Spain's Repsol has a 37.5% stake in the block and Bolivia's state-run energy company YPFB can take 82% of earnings on new energy production.

"This news is a surprise," said Bolivian President Evo Morales. "We had forecast 17 tcf through 2020 and Repsol's new discovery wasn't in our plans."

Bolivia now has 10.45 Tcf of proven reserves.

Natural gas accounts for roughly half of Bolivia's total exports, but its reserves have dwindled because of a lack of new finds and under-investment.

The discovery will likely ease worries about Bolivia's ability to honor export contracts and sustain its high levels of domestic spending.

Luis Alberto Sanchez, the country's energy minister, said the new find will likely add $1.3 billion to the government's annual oil and gas proceeds.

Bolivia earned $31.5 billion from its key energy sector between 2006 and 2015—600% more than in the previous two decades, according to official data.

Morales, who nationalized the energy sector in 2006, reiterated that the government will invest $2.4 billion in exploration and extraction this year.