Originally Posted by xliioper

If they are DL coded flights, then you use DL fare class table (even if operated by partner). DL uses P/A/G fare classes for for Premium Select/Premium Economy cabins (as noted above, KL is installing Premium Economy cabins in it's aircraft). KL uses W/S/A classes (same as AF) for Premium Economy classes even though their table on delta.com has not been updated yet. Note that KL does not have separate fare classes for it's Economy Comfort cabin (unlike DL Comfort+) and you can't buy DL Comfort+ fares on KL operated flights.