Place the oxtails and onions into a large mixing bowl, then drizzle the oil all over the oxtails.
Next make sure everything is nicely coated with the oil, then sprinkle the BBQ seasoning all over the oxtails.
Place the oxtails and onions into a large pot, and place the pot over medium-high heat.
Brown the oxtails and onions, then remove them from the pot, and place them into the slow cooker.
Go back to the pot that you brown the oxtails in, and pour in the chicken broth OR water.
Next add in the barbecue sauce, and liquid smoke.
Mix everything, an let cook for 5 minutes over medium heat.
Pour the barbecue sauce over the oxtails, then place the lid on the slow cooker.
Let cook on LOW for 6 hours.
Serve with your favorite sides.