Let me now turn to our enforcement activity with regard to airline marketing alliances, which are essentially joint ventures between airlines. These alliances fall somewhere between an outright merger and a traditional arm's-length interline agreement. Marketing alliances come in all shapes and sizes. Some may involve sharing frequent flyer programs or airport lounges. Occasionally, an alliance is accompanied by a stock investment by one airline in its partner.
Alliances can involve commuter carriers, domestic carriers, foreign carriers, or a combination.
Most of our experience with alliances between major airlines has been in the international marketplace, between airlines of different nationalities who may be restricted from serving each other's domestic markets. Alliances between major U.S. carriers, as distinct from alliances between hub carriers and commuter carriers that serve those hubs, are a relatively recent phenomenon. Other airlines, specifically American Airlines and US Airways, and United Airlines and Delta Airlines, also considered alliances last year, but appear to have shelved plans to code-share. Our analysis of a domestic alliance will be similar in most respects to our analysis of international alliances we have examined, so with a few exceptions that I'll point out, what I am about to say will apply in either situation. Alliances involving code-sharing are in many respects the most controversial.