Recently, a listener wrote in with a question about OPEC and oil prices. She was prepping for a camping trip… thinking about how much it costs to fill up her diesel-guzzling camper van at the pump. “It would be so awesome if you guys could do an episode explaining OPEC to us,” she emailed us. She wanted to know: why does OPEC exist? Why does it limit the supply of oil? And now that the United…