Will JetBlue be the next member of Oneworld?

American Airlines and JetBlue Airways announced this week they will extend their marketing partnership with 30 new interlining agreements and frequent-flier reciprocity. American adds 18 new cities to its route map, and JetBlue gets to offer its customers choice European destinations such as London, Paris and Rome.

The limited partnership has already led some observers to wonder if the two airlines are laying the groundwork for something more far-reaching — like bringing JetBlue into the Oneworld Alliance.

That would mark a huge step in the evolution of global alliances, which have traditionally shunned low-cost carriers due to concerns over corporate culture and quality control. Imagine the shock, for instance, if a Cathay Pacific frequent flier were to book on Spirit, expecting the two carriers to be similar in any way.

But JetBlue, Virgin Blue, Tiger Airways and a few other LCCs may rank high enough on the service ladder to overcome those objections. Does that mean an impending race to sign them up as alliance members?

In the U.S. and Europe, the answer is probably no – even if the alliances would like to answer yes.

The barrier is competition, not quality. In every recent merger or joint venture, regulators have cited fierce competition from LCCs as one of their reasons for allowing airlines to consolidate. Mixing network carriers and LCCs in the same alliance would undermine that logic, and competition watchdogs would immediately howl.

In the U.S., critics such as Rep. James Oberstar already are threatening to reverse 30 years of airline deregulation due to fears of excessive consolidation. Until those fears can be decisively — and statistically — answered, global alliances will likely remain the exclusive domain of network carriers.