Rinse the oxtails and pat them dry
Season with salt, black pepper, garlic powder, onion powder, paprika, and thyme
Heat oil in a heavy pot over medium-high heat
Brown the oxtails on all sides
Remove the oxtails from the pot
Add chopped onions, garlic, carrots, and celery to the pot
Cook until softened
Stir in tomato paste and cook briefly
Add beef broth, water, bay leaves, and Worcestershire sauce
Return the oxtails to the pot
Bring to a boil
Reduce to a low simmer
Cover and cook until tender, about 2.5 to 4 hours
Stir occasionally and add more liquid if needed
Add potatoes or beans if desired during the last hour
Taste and adjust seasoning
Serve hot over rice, mashed potatoes, or with bread