Preheat oven to 325 degrees F. Grease and flour 2 loaf pans.
Combine margarine, oil, bananas, and sugar.
Add eggs, one at a time, beating well.
In a separate bowl, sift flour, salt, and soda.
Add dry ingredients alternately with buttermilk to batter. Mix well.
Stir in nuts and vanilla.
Pour into prepared loaf pans. Bake for 75-80 minutes or until pick inserted in center comes out clean (22 minutes for mini loaves.) Freezes well and makes a nice gift!
VARIATION: Mix 1 1/2 teaspoons sugar and 1 1/2 teaspoons cinnamon together and sprinkle over top of loaves.