BUENOS AIRES (Reuters) - The governor of Argentina’s Neuquen province, home to the vast Vaca Muerta shale gas and oil formation, easily won re-election on Sunday, defeating a candidate allied with President Mauricio Macri and another with former President Cristina Fernandez.

Omar Gutierrez, of the Movimiento Popular Neuquino party, had 38.4 percent of the vote with three-quarters of ballots counted late on Sunday, official results showed, guaranteeing his re-election for four more years.

The decisive results soothed concerns of oil and gas interests in the sparsely populated but strategic province home to one of the largest non-conventional oil and gas formations in the world.

Argentina is seeking to double production in the region, courting private investment and priming competition as it aims to pump 260 million cubic metres of gas daily within five years.

Ramon Rioseco, an opposition candidate allied with Fernandez, garnered 24.9 percent of the vote. Fernandez was indicted last year on charges that her administration accepted bribes from construction companies in exchange for public works contracts. She has denied the charges.

Rioseco´s candidacy had prompted concerns of a rollback of Macri´s investor-friendly policies, although Rioseco had maintained he would respect contracts signed between the province and oil interests.

Third-place finisher Horacio Quiroga, of Macri´s party, received 16.7 percent of the vote.

Argentina´s economy is shrinking and the country has one of the highest inflation rates in the world, a predicament that has left Macri’s center-right government on the defensive.

The Neuquen election was the first in a busy season in Argentina, which will culminate in October in a presidential election that could pit Macri against Fernandez. The former president is now a senator and has yet to declare her candidacy.