Mix together warm water, yeast, sugar and salt. When yeast is dissolved, add oil. Combine soda with buttermilk and add to yeast mixture. Sift together flour and baking powder. Combine dry and liquid ingredients. Place in airtight (covered) container in refrigerator and use as needed. The longer this dough is kept, the better it is. When ready to use, preheat oven to 350� F. Place amount of dough you can lift with two teaspoons into each cup of greased muffin tins. Let rise until double in bulk. Bake at 350�F about 30 minutes, until brown.