Co-share advantages
 

Doing a fair amount of business travel between two cities, I am always monitoring the fares. When the sales are on, I book two or more trips at a time. The travel agency my company uses has a negotiated discount with CO and NW, roughly 21%. The TA will not book back-to-back tickets because it is against the airlines' "law".

Wanting to stay "legal", I book one trip A to B to A and another B to A to B, using a different carrier for each ticket. But, as it turns out, the CO flight is actually on NW metal. So I get 2 r/t tickets, back to back, all on NW and all legal. Isn't that interesting?

And if I really have the time to kill, I check the fares on each combination because sometimes a r/t on NW but using CO co-share numbers yields a lower fare.

There is a real potential problem when using back-to-back tickets with "partner" airlines, particularly if you apply the frequent flyer miles to a single program.

The practice of back-to-back ticketing is prohibited in the Contract of Carriage regardless of who the carrier is.

Obviously if you travel on different carriers it's pretty difficult for them to catch you, but if you are traveling on the same airline's planes and crediting the miles to the same account it's a different story.

snake recommends that you request a copy of the Contract of Carriage from both carriers to read when you are waiting for delayed flights, or when you are having trouble sleeping at night. It might be useful to prepare for the possibility of a call from the Revenue Protection Unit.