In a large bowl, cream together the brown sugar, white sugar, and vegetable oil until light and fluffy. Add the eggs one at a time, beating well with each addition, then stir in the vanilla. Combine the flour, baking powder and salt; stir into the creamed mixture, then mix in the rolled oats. Cover and chill for at least 2 hours.
Preheat oven to 350 degrees F (175 degrees C). Grease cookie sheets.
Roll cookie dough into walnut sized balls, roll the balls in the confectioners sugar to coat, and place 2 inches apart onto the prepared cookie sheets.
Bake for 8 to 10 minutes in the preheated oven. Allow cookies to cool on baking sheet for 5 minutes before removing to a wire rack to cool completely.
