The application of two or more policies’ limits to a single occurrence or claim. This is common with product liability, construction defect, and pollution claims in which the occurrence has transpired over numerous years, and it is difficult to ascertain which policy provides coverage. It can also occur under auto liability or uninsured motorists (UM)/underinsured motorists (UIM) coverage in the business auto policy (BAP) or the personal auto policy (PAP) when two or more vehicle limits can be stacked to apply to a single occurrence.