Originally Posted by
mmradio
I have more than 100,000 miles combined on Delta, continental and Northwest. Can I combine them all together to upgrade on an international continental flight?
No. You have to redeem them from each carrier individually.
The closest you can get is that I believe you could use CO and NW miles to redeem one-way upgrades on a r/t ticket, so long as you had sufficient points in each of the two accounts for one of the upgrades, but I'm not 100% certain of this.