BUENOS AIRES (Reuters) -Argentine drivers ran the gauntlet on Monday to find scarce supplies of petrol to fill their tanks amid the most acute shortage in years, which has left many filling stations out of supply and long lines at any pumps still operating. The South American country, a major shale oil and gas producer, has suffered shortages of petrol and diesel since late last week because of domestic refining problems and as a lack of dollars has delayed imports. That has sparked anger at the government ahead of a second-round presidential election runoff next month between the ruling Peronist coalition's economy chief Sergio Massa, seen as the front-runner, and radical libertarian Javier Milei.