Around the world, many airlines belong to one of three large international alliances. These alliances extend airlines' reach to foreign destinations while encouraging flyers to stay within network. Three of the United States' largest airlines have joined alliances:

  • American Airlines is part of Oneworld
  • Delta Air Lines is aligned with SkyTeam
  • United Airlines is with Star Alliance

While alliance members honor each other's frequent flyer rewards program numbers, keep in mind that alliance airlines aren't always your least expensive or most expedient itinerary option.

U.S. Airlines And Code-Sharing Partnerships

Instead, some airlines negotiate code-sharing partnerships with other airlines. By listing flights under each other's names, airlines expand flight choices and usually honor to some degree frequent flyer and rewards programs:

1. Alaska Airlines partners with both Delta and American as well as Aeroméxico, Air France, British Airways, Cathay Pacific, Emirates, Fiji Airways, Hainan Airlines, Icelandair, Japan Airlines, KLM Royal Dutch Airlines, Korean Air, LATAM Airlines, Qantas, PenAir and Ravn Alaska.

2. Hawaiian Airlines partners with Korean Air, All Nippon Airways, China Airlines, JetBlue, Virgin America, Virgin Atlantic and Virgin Australia.

3. JetBlue partners with Emirates, Hawaiian Airlines, JetSuiteX, Silver Airways, Singapore Airlines and South African Airways.

4. Virgin America is slated to merge with Alaska Airlines in 2017. In the meantime, it partners with Virgin Australia, Virgin Atlantic, Emirates, Hawaiian Airlines and Singapore Airlines.

Yet again, however, these may not be your least expensive option.

U.S. Airlines That Operate Alone

A handful of U.S. airlines operate solo, their focus on keeping costs low budget-conscious flyers who are always on the lookout for cheap flights. Their rewards partners are within the hotel, car rental, credit card and merchant realms:

5. Allegiant serves Puerto Rico, Hawaii and cities within the continental United States. It doesn't offer a frequent flyer program, but myAllegiant rewards program members can earn points through the Allegiant World MasterCard and qualifying Allegiant-booked travel.

6. Frontier Airlines serves U.S. destinations, Mexico, the Dominican Republic and Jamaica. Frontier Elite status comes with priority services such as advance seat assignments. Members of Frontier's EarlyReturns reward program earn miles through Frontier-booked travel with Frontier partners and the Frontier Airlines World MasterCard.

7. Southwest flies to U.S. cities, Mexico, Latin America and the Caribbean. For frequent flyer priority services, Southwest offers A-List, A-List Preferred and Companion Pass elite levels. Rapid Rewards program members earn points through fares, Southwest's Rapid Rewards VISA Card or its other partners.

8. Spirit covers the continental United States, Mexico, Central and South America, the Caribbean and parts of Canada. Frequent flyers progress through three status tiers: Somebody, Elite and VIP. Free Spirit rewards program partners include hotels, car rentals, Spirit Cruises and the Spirit World MasterCard.

9. Sun Country serves most major U.S. cities, with additional destinations in Alaska, Mexico, Costa Rica and the Caribbean. Elite Ufly status earns priority services. Its Ufly rewards program awards 10 points for every dollar spent on flights, upgrade fees, vacation packages or other qualifying purchases, but partner choices are limited.

Since travelers have a ton of options and airlines continue to shift, always present your frequent flyer number. On the right day, it might just count!