Preheat oven to 375 degrees F. Line muffin cups with cupcake liners.
In large bowl, whisk together oil, eggs, milk, sugar, and vanilla.
Whisk in flour, cocoa powder, baking soda, and salt until just combined.
Gently stir in sour cream.
Stir in 1 1/2 cups of chocolate chips.
Spray cupcake liners with nonstick cooking spray. Then fill each muffin cup 3/4 full with muffin batter. Sprinkle remaining chocolate chips on top.
Bake for 18-20 minutes.