Crude is easier to extract, but if it "ever" gets scarce,,, we have an alternative...
At 3.3 trillion tonnes, the oil shale deposits in the United States are easily the largest in the world. There are two major deposits: the Eastern US deposits, located in Devonian-Mississippian shales, cover 250,000 square miles (650,000 square kilometers). The Western US deposits, the Green River formation in Colorado, Wyoming and Utah, are among the richest oil shale deposits in the world.
flying..lol birds fly long distances just gliding on air currents. no energy at all. theres no reason a plane cant do the same for say 200miles or so.with a very small engine to climb high enough.if the planes made right. holding under 40passenges n no cargo. maybe a 55gal fuel tank. for emergencys. to fly between say newyork n phil. or boston.or wash dc. pitts n chicago.neworleans n houston. or inside cali. closer cities. every jet dont haveto wiegh 50000tonnes. some can wiegh under say 5tonnes or 8 tonnes.