Combine yeast and warm water in a small mixing bowl, stirring to dissolve; let stand 5 minutes or until bubbly. Add buttermilk and oil to yeast mixture; stir well.
Combine dry ingredients in a large bowl. Add buttermilk mixture, stirring with a fork until dry ingredients are moistened.
Turn dough out onto a floured surface, and knead 3 to 4 times.
Shape dough into 2-inch balls; place 1/8-inch apart in three well-greased 9-inch cast iron skillets. Cover and let rise in a warm place (85°), free from drafts, 1 1/2 hours or until doubled in bulk. Bake at 425° for 12 minutes or until golden brown.
Note: Biscuits may be placed in greased baking pans to rise and bake.