Any flight that isnt marketed by DL (meaning the flight number you book doesn't start with DL, even if the flight is operated by DL) earns MQD as a percentage of miles flown . This is due to fact DL doesnt know exactly what was paid. For certain close partners (AF/KL/VS/MU/KE) this can result in huge amounts of MQD on long flights. MU is generally one of the best, they have cheap business class tickets (approx $2k-$3k range) US-ASIA/INDIA/AUSTRALIA/NZ that thus earn MQD two or three times what you actually paid.