1. Heat the vegetable oil in a large pot over medium-high heat.
2. Brown the oxtail pieces on all sides, then remove from the pot and set aside.
3. In the same pot, add the chopped onion and garlic, and sauté until softened.
4. Add the thyme, allspice, salt, and pepper, and stir well.
5. Return the oxtail to the pot, add the beef broth, and bring to a boil.
6. Reduce the heat to low, cover, and simmer for about 3 hours, or until the oxtail is tender.
7. Add the butter beans and cook for an additional 15 minutes.
8. Serve hot with rice or your favorite side dish.