Flights to Latin America produced the highest operating margins of any region for U.S. carriers in 2011 and the first quarter of 2012, and the margin has continued to improve even as capacity rises.

Latin America services produced an 8% operating margin in 2011, based on quarterly financial data the airlines are required to file with the U.S. Transportation Department. That compared to a margin of 5% for domestic services, 3% for Pacific operations and negative 6% for transatlantic.

Similarly, the 5% margin for the first quarter topped a 4% margin for domestic operations and losses on Atlantic and Pacific services.

The Form 41 financial data filed with the DOT are not a perfect measure because many international itineraries include a domestic portion, so airlines can differ in how they decide to allocate that revenue in their reporting. But it does indicate the relative strength of the regions.

Of particular interest is the margin produced by United Airlines since it merged with Houston-based Continental Airlines, which converted a run of negative or single-digit margins into a 22% margin for 2011 and 18% for the first quarter of 2012. That compares with margins of 17% for routes serving the Pacific region, 12% for the Atlantic sector and 1% for domestic routes for an airline that has vocally opposed the proposed introduction of Southwest Airlines services to Latin America and the Caribbean from Houston.

JetBlue Airways, which has boosted Latin America and Caribbean services to nearly 30% of its capacity, reports a 27% margin for the region in 2011 and 22% for the first quarter 2012. That compares with 3% and 4%, respectively, for its domestic services. The annual margin has climbed every year since the first full year of service to the region in 2009.

The carrier most heavily invested in the region, American Airlines, also produced positive returns from Latin America, in sharp contrast to its other sectors. Its 8% margin in 2011, for example, compares to negative margins of 30% for the Pacific, 19% for the Atlantic and 4% for domestic.

One apparent exception to the Latin America bounty is Delta Air Lines, which has rarely reported even a quarterly operating profit on its Latin American services in the past decade.