Preheat oven to 400 degrees. In a bowl, combine flour, sugar, cocoa, baking powder, baking soda, and salt. Make a well in the center. dd oil, vanilla, vinegar, and warm water. Stir just until moist. Add hocolate chips. Spoon batter into prepared muffin tin (use cupcake papers), filling 3/4 full. Bake for 15 - 20 minutes.