95b323b7_of_Size__Policies___Yahoo_News__Stated_policy
[Airline] Delta [Costs] The airline does recommend that you purchase an additional seat in advance if you think that you might need one and cannot afford to wait around for a flight with empty seats. None specified. [Stated policy] 
Passengers are NOT required to purchase additional seats based on size, but you may be asked to move or wait for the next flight with additional seating space.
Airline "Customer of Size" Policies - Yahoo News
Stated policy