Turbulence has returned to the oil market this year. Oil prices have tumbled more than 15%, weighed down by the uncertain impact of tariffs and other factors. As a result, the price of the global oil benchmark Brent, which spent much of the past couple of years bouncing around in the range of $75 to$85 a barrel, has slumped down closer to $60 a barrel. Lower crude prices are a problem for many oil producers. However, they're not an issue for ExxonMobil (XOM -0.10%). The oil giant has spent several years bu ...