Measure buttermilk and set it on the counter to come to room temp.
Preheat oven to 425 degrees F. Line two muffin tins with 15-20 paper liners. You can add more or less liners when filling.
Place ripe, peeled bananas in a large bowl and mash with a fork and/or potato masher until well mashed.
Mix in vegetable oil and melted butter.
Add granulated and brown sugars and stir well.
Add eggs, vanilla, and buttermilk. Stir well.
In a separate bowl, stir together flour, baking powder, baking soda, and salt.
Add dry ing. to wet ing. and mix with a large fork or a spatula JUST UNTIL COMBINED, and no more streaks of flour remain. Don't overmix.
Fold in chocolate chips.