Heat the vegetable oil in a medium pot over medium heat. Add the onion and garlic and cook about 5 minutes. Stir in the ketchup, vinegar, brown sugar, steak sauce, Worcestershire, molasses, mustard, salt, celery seed and 1 cup water. Bring to a boil, then reduce the heat to medium low and simmer until the onion is tender, about 15 minutes. Stir in the liquid smoke. Strain the sauce, pressing on the solids to extract any liquid.