Mix flour and oil together in a heavy ovenproof container. Place on center shelf in preheated 400 degree oven. Bake at this temperature for 1 1/2 to 2 hours. Set timer, and stir roux every 15 minutes. Roux should be a caramel color when done. Remove from oven, cool, transfer to containers with tight fitting lids and store in refrigerator until needed. Roux may also be frozen. Yield: enough for 4 to 6 pots of gumbo.