Preheat oven to 350 degrees F.  Line a muffin tin with paper liners.

In a large bowl, stir together the oil, espresso, bananas, and vanilla.  Stir in the flour, carob or cocoa, and baking soda.  Stir in the carob or chocolate chips.  Spoon the batter into the liners, and bake about 20 minutes until risen, set, and a toothpick inserted in the center comes out clean or with a few moist crumbs.

Serve warm or cool completely in the pan.  Muffins may be stored in an airtight container at room temperature for up to 4 days or frozen, wrapped in parchment and foil and placed in a zipper bag for up to 3 months.  Thaw in the microwave 1 minute or at room temperature about 2 hours.