Preheat the oven to 350°F. Sift together the flour, baking soda, and salt. In another bowl, cream the oil and sugar. Add the eggs, bananas, and buttermilk; beat well. Stir into the dry ingredients, then stir in the nuts. Pour into a greased 9x5-inch pan. Bake for 1 hour, or until a toothpick inserted in the center comes out clean. Cool for 10 minutes in the pan, then remove from the pan and cool completely on a wire rack.