Put oven rack in middle position and preheat oven to 350F. Grease muffin tin with oil or use a non-stick baking spray or use liners.
Whisk together flour, baking powder, baking soda, salt and pumpkin pie spice in a small bowl.
Whisk together pumpkin, oil, eggs, sugar in a large bowl until smooth, then stir in flour mixture just until combined.
LAZY STEP: Sometimes when I'm in a hurry I will mix the liquid ingredients in my mixer first and then add the dry ingredients into the wet ingredients directly. I know I'm a rebel but they still come out just fine. still recommend mixing separately if you can!
Divide batter among muffin cups (each should be about ½ - ¾ full)
Bake 20-25 minutes, until puffed and golden brown and a wooden pick or skewer inserted into the center of a muffin come out clean. I always tap the tops and if the tops are firm but springy, they are done.
Cool in pan on a rack 5 minutes, then transfer muffins from pan to rack and cool to warm or room temperature.