Speculation grew last week that Delta Air Lines, US Airways or some buyout group may try to buy American Airlines, which went into bankruptcy in November to reorganize under Chapter 11. If Delta were to buy American, once the nation’s largest carrier, it would almost certainly invite intense scrutiny from regulators. The resulting mega airline would be such a huge force in the marketplace that it could mean service cutbacks.

A Delta-American merger would mean that two major carriers -- the other being United Airlines, which just absorbed Continental Airlines -- would control 55 to 60 percent of the market. Southwest Airlines would be a third with about 20 percent of domestic traffic. But it has few overseas routes, while a Delta-AA combination would offer extensive route networks to Europe, Latin America and Asia.

US Airways also is reportedly considering buying American. Speculation about that deal has been around for a while, but many industry observers don’t consider that the two would be a good match.

Yet another contender for American is TPG Capital, which in the past has had a stake in other airlines, including America West (which acquired US Airways and then took its name) and Continental.

Any such deal is far in the future, in part because of the circumstances that led American to declare bankruptcy. American is the last of the major carriers to finally declare bankruptcy in order to try to return to profitability by ridding itself of debt. Earlier efforts to stave off bankruptcy such as winning concessions from its unions in 2003 have not been enough to help the carrier, the only major not to see profits in the past few years.

At first glance, regulatory approval of a Delta-AA deal would seem unlikely, but regulators tend to look at these deals on a route-by-route basis as opposed to the total market. American may be staggering, but it remains the world’s third-largest carrier when measured by passenger traffic. If bankruptcy allows it to shed its debt, it could become far more attractive to other airlines.

American’s parent company, AMR, has said that staying independent is American’s best course. Rather than merge with another airlines, it has been building many new relationships with a variety of domestic and international carriers -- it has deals with both Jet Blue and airberlin, and has a three-way joint venture with British Airways and Iberia, for example.

Such partnerships, in which airlines coordinate scheduling to make codesharing easier and offer each other’s loyalty club members at least some reciprocal benefits, are one way of getting some of the benefits of a merger without actually merging. American is also part of the oneworld alliance. This is another way in which airlines seek to reap some benefits from partnerships with other airlines by codesharing. Iberia and BA are also part of oneworld.

Delta, on the other hand, is in the Skyteam airline alliance and US Airways is in the Star alliance. Presumably if American were to be sold, it would be absorbed into the acquiring airline’s alliance, creating a void in oneworld, which has to have a strong U.S. domestic partner to feed its partner airlines’ overseas networks.

The airline industry has been consolidating for decades. Consumer advocates see problems with that -- having a few big players lessens competition, raises prices and often decreases choices for travelers. At the same time, aviation is struggling and a healthy aviation system is essential for world economies. Airlines are uniquely vulnerable to swiftly changing and often harsh geopolitical winds.

Some of their woes are self-inflicted -- for decades they sought to move market share through expensive loyalty programs and bloody fare wars. Yet soaring oil prices that are not always driven by the laws of supply and demand but by market speculation cause airlines serious pain. They have dramatically restructured their fleets, but that’s another enormous expense. And airlines are trying to do business in a world economy that has struggled through a historic crash, followed by an uncertain recovery now under threat from the current Eurozone crisis.