Heat oven to (450°F). Combine flour, oats, sugar, baking powder, baking soda and salt; mix well. Cut in margarine with pastry blender or two knives until mixture resembles coarse crumbs. Add buttermilk; mix with fork just until dry ingredients are moistened. Drop by (1/4 cup) measure onto ungreased baking sheet. Beat together egg white and water. Brush tops of biscuits with egg white mixture. Bake 10 to 12 minutes or until light golden brown. Serve warm. *Or substitute soured milk. Combine (1 1/4 cups) 1% milk and (4 tsp) lemon juice; let stand 5 minutes or until slightly thickened.