Rub the roast with the oil.
Place in a roasting pan on a rack and bake at 350 degrees for about two hours.
Meanwhile, in a small bowl combine the pineapple preserves, horseradish, and mustard, mixing well.
Turn the roast and brush with the pineapple mixture.
Continue roasting thirty minutes longer or until the meat is tender, nicely browned and glazed.
Place the remaining sauce in a bowl and serve with the roast.