The Mississippi River is known as the Middle Mississippi from the Upper Mississippi River's confluence with the Missouri River at St. Louis, Missouri, for 190 miles (310 km) to its confluence with the Ohio River at Cairo, Illinois. The Middle Mississippi is relatively free-flowing.
As Hopper notes, eight major U.S. airlines offer free cancellation for tickets purchased at least seven days in advance: Delta, United, US Airways, JetBlue, Southwest, Spirit, Frontier and American (in American 's case, you'll hold your ticket instead of purchasing it).
Cancellations by Traveler. Southwest will allow reservations to be canceled without penalty if the passenger calls or cancels online within 24 hours. A refund will then be processed in the form of payment of the ticket purchase. Cancellations Within Airline Control.