BUENOS AIRES (Reuters) -Drilling and fracking activity in Argentina's Vaca Muerta, the world's fourth-largest unconventional oil reserve, is plateauing due to lower oil prices and rising costs, a slowdown that could complicate the political agenda of libertarian President Javier Milei. The huge Vaca Muerta formation in western Argentina accounts for 64% of the country's oil production even though only 8% of it is under development. It is vital to Argentina's economic future and Milei's government, whic ...