Season the oxtails with salt and pepper, then gently cover them with flour.
In a large saucepan, heat the olive oil on medium-high. Cook the oxtails on all sides until browned. Remove and set aside.
In the same saucepan, sauté the onion and garlic until tender.
Return the oxtails to the pot. Combine the beef broth, red wine, carrots, celery, bay leaves, thyme, and Worcestershire sauce.
Bring to a boil, then turn the heat down to low. Cover and simmer for 3-4 hours, or until the meat is tender and falling off the bone.
Remove the bay leaves and serve the oxtails with their gravy.