Originally Posted by xliioper

No, there is nothing wrong or any violation of ticketing rules with booking as two one-ways instead of a roundtrip. There can be a benefit for booking AM coded flights for premium cabin fares due to MQD/Miles earning based on distance. For coach class fares, not so much (particularly on expensive coach class tickets where DL earn based on spend may come out ahead). You will need to look at distances and fares classes to determine which one is better. Open jaws to Mexico should still qualify for cheaper roundtrip fares (as long as jaw distance is shorter than either of the two flown legs). But without know routes and dates, it's hard to say why it is pricing this way.