Preheat oven to 325 degrees F (165 degrees C). Grease and flour an 8x4 inch loaf pan.
In a separate bowl mash bananas to equal 1 cup and add oil, eggs, buttermilk and vanilla extract. Beat together and pour this mixture into the dry ingredients. Add nuts and stir just until combined. Pour batter into 8x4 inch loaf pan.
Bake for 1 hour and 20 minutes in the preheated oven, or until a toothpick inserted into the cake comes out clean.