Heat the oil in a large heavy pot and add the flour. Cook the roux, stirring constantly, to a light brown if you want it Creole-style, and to a dark, almost milk chocolate color if you want it Cajun-style. Just before the roux reaches the proper color, add the vegetables and stir like hell, being careful not to spatter yourself. When the vegetables are tender, add the stock, salt, and peppers. Stir until the roux is dissolved, and simmer over low heat for one hour.
Add the seafood about 5 minutes before serving, and cook over low heat just until the shrimp turn pink. Serve over rice.