Preheat oven to 350°F. Spray a 13 x 9-inch baking pan with cooking spray.
Mix butter, brown sugar, flour and oats until crumbly in a large mixing bowl. Press into baking pan. Bake for 10 to 12 minutes or until lightly browned.
Beat eggs, corn syrup, sugar, butter, vanilla and peanut butter in a large bowl with an electric mixer. Stir in pecans and butterscotch chips with a spoon. Pour mixture over crust. Bake for 25 to 30 minutes or until filling is set.
Remove from oven and cool. Refrigerate until firm, about 1 hour.