Not sure if still continuing, but you get double CO miles on Midway Airlines. Anyone remember the expiration date?

For use of miles, depends where you fly. With NW, you can use miles on partner KLM. With CO, you can't. Domestically, they are the same parnters and codeshares with each other.

CO offers more mileage bonus opportunities. Others may disagree, but I have been happy with the unlimited standby electronic upgrades offered by CO for elites, even if you are Silver!

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"Fly me to the moon and let me earn alot of miles."