KLM code share
 

I have a KLM credit from a cancelled flight. It is valid on any flight marketed by KLM (in other words, any flight with a KLM flight number), even if not using KLM metal. I have no plans to fly KLM before the credit expires, but I could use this credit on a DL-operated flight if it has a KLM flight number. Is there some easy way to find out which DL flights have KLM (code share) flight numbers? Is the only way to do this to do searches on KLM's website? Thanks for any advice.

Many/most transatlantic DL-operated flights have a KL code share. As far as I know, KL-numbered, DL-operated flights in the US are available only in conjunction with a transoceanic segment operated by KL/AF/DL. Code shares are best found on the KLM website, or by giving KLM a call when you know where/when you want to travel.

Call DL. Ask to be transfered to the KL support desk as you have a KLM credit need yo use to book DL flight. Agents can book using credit there. You'll get a KLM ticket with DL flight number.

Does that work for any DL flight, or only for flights that have both KL and DL flight numbers (code shares)? Thanks.

All DL flights have a KL/AF codeshare number available. They're just not published with inventory. One codeshare number can even be used for multiple partner operated flights on the same day. i.e. KL9876 could be used for two totally different DL flights on exactly the same day. (totally different routes even)