Most of the oil is on the middle part of the lane. From about the second arrow to the gutter, less oil is present. This allows for more hook on the ball.
If you throw on the outside area, the ball hooks toward the pocket. If you throw toward the center of the lane, the oil keeps the ball headed toward the pocket.
Occasionally the opposite happens where the oil is more on the outside so an adjustment would be necessary.
Sometimes the entire width of the lane will be oily, an adjustment would need to be made for this.