Why did the airlines suddenly raise the prices of multi-city trips by such a high margin?

Great question! Several weeks ago American, Delta, and United implemented new rules that prevent many one-way fares from being combined which has driven up the cost of multi-destination trips by as much as a factor of 7. Initially, the airlines each offered explanations that were a version of “… implemented to ensure that the fares we make available in the marketplace are consumed as intended….” Following uproar from the travel industry and the traveling public these airlines have admitted that the new rule has had “unintended consequences” and they are “reviewing the situation.” So far, we have seen only the most minimal remediation, though we remain hopeful that the airlines will bow to pressure and modify or reverse the new rules in the near future. In the meantime, travelers booking with knowledgeable agencies such as Travel-On are protected from the grossly inflated fares. Travelers booking on public or airline websites have little recourse as those sites are unable to price a single trip as multiple tickets.