Most American refineries are set up for the kinds of heavy, sour crudes you get from Canada, Mexico and Venezuela. That made sense when it looked as if the U.S. was running out of domestic oil, but then came the shale oil revolution. American shale oil, it turns out, is typically light and high quality, meaning it is not best-suited for domestic refineries. The upshot is that while arithmetically America is energy independent—producing far more oil than it consumes—in practice it is anything but. It must keep sucking in heavy oils from elsewhere to feed its refineries while sending Texan crude
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