In a constantly changing airline industry, there are always some carriers that act as catalysts for wider upheaval. Aviation Week's commercial editorial team has assembled this list of 25 carriers that are the main contenders to fulfill this role in 2013. Many on the list are poised to make major advances that will present new challenges for their competitors, some will influence the industry as they disintegrate, and others are reaching an inflexion point where either outcome is possible. Wherever they fall on that spectrum, these are the airlines that are likely to provide the industry's biggest talking points over the next year.

Delta Air Lines will be in the spotlight in 2013 due to its acquisition of a Pennsylvania oil refinery as a hedge against the widening spread between crude oil prices and jet fuel costs. Airlines will be watching to see if the move really does produce at least $300 million in savings, as the carrier estimates. Delta is also at the forefront of the shake-up in the U.S. regional airline industry, with plans to remove at least 200 of the 325 50-seat aircraft in its network by 2015. Its plans for achieving these cuts should become clear by early next year. Delta drew even more attention last week when it agreed to purchase a 49% stake in Virgin Atlantic, boosting its access to London's Heathrow Airport.

Southwest Airlines acquired AirTran Airways in May 2011, but it will be in 2013 that the real impact of that acquisition will start to become clear. Customers will be able to book single-ticket itineraries by March, connecting Southwest and AirTran networks for the first time, and Southwest is expecting this to significantly boost revenue and give it a competitive advantage. Southwest also faces some new challenges, with CEO Gary Kelly warning that the carrier must respond to the cost-cutting that American Airlines and other competitors have achieved in bankruptcy protection. That raises the prospect of a problem Southwest usually does not encounter: divisive disputes with its labor unions.

American Airlines is likely to emerge from Chapter 11 bankruptcy protection in 2013, but in what form? US Airways is pushing for a merger, but American's management has long stated its preference to emerge as a standalone carrier, focused on high-value business routes from its hubs in Chicago, Miami, Los Angeles, Dallas/Fort Worth and New York. A merger with US Airways would create an airline with a strong presence on the U.S. East Coast and Midwest, Europe and Latin America. American's three unions have thrown their support behind the deal, saying the carrier will not be able to compete with rivals Delta Air Lines and United Airlines without merging with US Airways.

Pinnacle Airlines will be the focus of the U.S. regional airline industry in 2013. Operating under Chapter 11 bankruptcy protection since April 2012, Pinnacle's reorganization will have a major bearing on the future of rivals SkyWest Inc. and Republic Airways, which are both anticipating a sharp reduction in Pinnacle's operations. It is likely that Pinnacle will bear the brunt of partner Delta Air Lines' planned cuts in regional jet requirements, and the carrier has already shed its contracts with other major airlines. There may still be a future for Pinnacle if its pilots agree to an extensive concessions package, although the likelihood is that the carrier will become another victim of consolidation.

The coming year will be another period of international growth for Hawaiian Airlines, as it continues to look to Pacific Rim nations for new opportunities. It will launch flights from Honolulu to Taiwan and New Zealand in 2013, and nobody would be surprised to see other new destinations also added. This follows the recent expansion of services to Australia, and new routes to Japanese cities and South Korea. All of this is part of Hawaiian's plan to reduce its reliance on the highly competitive routes from the Western U.S. to Hawaii. The airline will also be looking to increase its coverage of its local market, as it plans to launch a new regional turboprop subsidiary.

WestJet is looking to give Air Canada a run for its money next year. The launch of a new regional feeder operation called WestJet Encore is sure to heighten domestic competition. Encore intends to reach smaller communities, and the carrier says fares could dip 50% below those charged by rivals on comparable routes. Could a price war result? The answer to that will become apparent when Encore launches in the second half of the year. One thing that does seem certain is WestJet's commitment to the venture, with 20 Bombardier Q400s on firm order and options for 25 more. The Canadian low-cost carrier has been vocal about the advantages of Encore over competitors, but it will soon be up to consumers to decide.

Air Canada will make an aggressive push into new international markets next year—if all goes as planned. The carrier is awaiting government approval to begin non-stop Toronto-Istanbul service on June 4, as a gateway to Turkey, Central Asia, the Middle East and Africa through a code-share with Turkish Airlines. This expansion could prove particularly valuable for Air Canada as competition stiffens on its home front, where WestJet's planned new regional operation could significantly undercut Air Canada's fares. Although Air Canada remains confident that its hold in domestic markets will remain strong, the new international markets could be important to its fortunes in 2013.

The merger of Chile's LAN Airlines and Brazil's Grupo TAM in 2012 created Latam, one of the world's largest carriers by market capitalization, and furthered airline consolidation in Latin America. Latam expects demand to remain strong throughout South America and is adding capacity in the region. The carrier is taking a page out of the low-cost-carrier playbook and altering its product on short-haul regional routes to compete more effectively with startups and LCCs. The one blight on the forecast is Brazil, where domestic demand has cooled. TAM is shifting its focus to international routes and pulling capacity out of its domestic Brazil operations, but it is poised to grow, should demand recover.

Whether Mexicana DE Aviacion finally emerges from bankruptcy protection and resumes operations is the story to watch in Mexico this year. Newly inaugurated Mexican President Enrique Pena Nieto vowed on the campaign trail to resurrect Mexicana, but it remains unclear if he will make good on that promise. A bankruptcy court dismissed an investment group that had pledged to recapitalize the airline, and although several investors have expressed interest, the court has yet to approve a new restructuring plan. Since Mexicana's grounding, Interjet has emerged as the country's largest domestic carrier and, along with Volaris and Aeromexico, it has filled the gap left by Mexicana.

A major overhaul of Qantas's international operations is going to have serious ramifications for the other big players in Australia's long-haul markets next year. The most significant change will see Qantas partnering with Emirates, giving the pair a more dominant position in the highly contested Australia–Europe market. The link-up will enhance Qantas's network into Europe but will make life more difficult for carriers, such as Singapore Airlines, that draw a lot of revenue from the so-called Kangaroo routes. Next year will also be important for Qantas low-cost subsidiary Jetstar, which is due to take delivery of the first of its 15 Boeing 787-8s.

Jetstar Japan is on this list as a proxy for the three Japanese low-cost carriers that were established in 2012—the other two being Peach and AirAsia Japan. LCCs are a relatively new phenomenon in Japan, and while their fleets of narrowbody aircraft are still small, they are already having an impact on the market. This will be amplified in 2013 as they add new aircraft and continue their expansion into domestic and international markets. Peach and AirAsia Japan were set up as joint ventures by All Nippon Airways, while Japan Airlines set up the Jetstar Japan joint venture. The coming year will provide more clarity on how much traffic the upstarts will siphon from their mainline parents.

China's Spring Airlines is a budget carrier that is a potential threat to the lumbering state airlines, with service and cost levels closely matched to the needs and wallets of Chinese fliers. The experience of low-cost carriers in Southeast Asia suggests that China is superb territory for this model: Income levels there, though varying by region and city, compare closely with those of Indonesia, Thailand and Malaysia, where budget carriers have become dominant. So far, Spring has not been able to realize anything like its growth potential, as it has only about 30 Airbus A320s. But with a new administration taking control in Beijing, market-based reform in aviation could yet appear—to the benefit of Spring.

Tianjin Airlines is the leader in the current fad of subsidized local subsidiaries of Chinese mainland airlines. It is an offshoot of Hainan Airlines backed by the Tianjin city government. Since Tianjin Airlines was formed in 2009, such carriers have been popping up all over China. How big can they grow? Pretty big, if the ambitions of Tianjin Airlines are anything to go by. Originally an operator of Embraer ERJ regional jets, the carrier now uses mainly Embraer 190s, has begun introducing Airbus A320s and has plans for A330s that it could fly on intercontinental routes. Tianjin is a large and well-developed city, and many others are following its example with locally based subsidiaries of the major carriers.

The AirAsia group appears set to make acquisitions next year so it can expand its footprint farther across Asia. Possible takeover targets include Zest Air in the Philippines and T'way and Eastar in South Korea. The group is also believed to be eyeing potential opportunities to launch a carrier in Cambodia. To help fund its expansion and boost its balance sheet, AirAsia plans to float some of its businesses. Its Kuala Lumpur-based, medium-haul low-cost carrier AirAsia X aims to have an initial public offering early in 2013 on the Kuala Lumpur stock exchange. AirAsia also wants to float its Indonesian affiliate, Indonesia AirAsia, on the Jakarta stock exchange.

Lion Air is set to shake up Southeast Asia's airline industry next year. Its Malaysian affiliate Malindo Airways is due to start flying in the first half of 2013 and will compete head-to-head against Malaysia's AirAsia. Malindo may also capture some traffic from Malaysia Airlines, because Malindo will offer frills such as free checked baggage and inflight entertainment. Lion also recently established a Singapore-based aircraft leasing company called Transportation Partners. The airline has a large order-book for 737-900ERs and Boeing 737 MAX aircraft, and Transportation Partners' remit is to secure aircraft financing and place some of these aircraft with other carriers around the globe.

Singapore Airlines (SIA), under CEO Goh Choon Phong, has been transformed from a carrier focused on the premium segment to an airline group with a range of brands for different market segments. No longer content to be reliant on the slow-growing premium business, the group aims to tap into all market segments with its portfolio: SIA mainline (premium), SilkAir (premium short-haul), Tiger Airways (low-cost short-haul) and Scoot (low-cost medium-haul). Tiger and Scoot plan to add aircraft next year, as does SilkAir. In terms of route expansion, China will be a key focus for the group in 2013. It may also look to strengthen relations with Star Alliance partner Air China as another means of accessing China.

Africa's first low-cost carrier, Fastjet, achieved a load factor of 78% on Nov. 28—not bad for its first day of operations. But the jury is still out as to whether the low-cost model will work in Africa, or if the lack of infrastructure and liberalization as well as political opposition will prevent it from becoming as successful as it is in most other parts of the world. Fastjet plans to operate up to 15 aircraft by the end of 2013 and wants to expand beyond its initial base in Tanzania, at least to neighboring Kenya. But the real breakthrough will come if the airline becomes established in the south and west of Africa.

Ethiopian Airlines, based in one of the world's poorest countries, has had an impressive track record in recent years. It joined the Star Alliance and became the first African airline to take delivery of the Boeing 787. Now, with its 787 fleet growing, Ethiopian has to make the next transformation—upgrading its onboard product to industry-standard levels. The airline aims to build a long-haul network between Africa and Asia, so it must compete not only with the onboard products of Asian airlines, but also with those of the big three Persian Gulf carriers. In its efforts to quadruple sales by 2025, Ethiopian also has to further develop its African network and its Togo-based affiliate, ASKY Airlines.

The coming year will be pivotal for South African Airways as it looks to establish its future direction. The airline is in a leadership crisis once again, following the departure of CEO Siza Mzimela in late 2012. South Africa's government has also had to inject a further 5 billion rand ($576 million) into the airline to keep it afloat. The carrier now has to find a new CEO who can craft a strategy that will turn it into a sustainable business again. SAA has to determine where it can grow and how it can participate in the expected development of air transport in the continent. It is looking again at joint ventures in other African countries such as Ghana, although previous efforts have failed.

Qatar Airways prides itself on its five-star service levels, although until now that description would not have applied to its main hub airport. The terminals at Doha are nice, but with no contact gates available, all passengers have to be bused across the airport, sometimes with multiple stops. That will all soon change when the New Doha International Airport (NDIA) opens in 2013. The exact opening date has not yet been made public, following delays in the completion of lounges in the terminal. But once NDIA is ready, Qatar Airways will for the first time have a home base that is designed for connecting traffic.

Etihad Airways has bought shareholdings in Air Berlin, Aer Lingus, Air Seychelles and Virgin Australia, and if CEO James Hogan has his way, this is only the beginning. Etihad appears to be preparing to pursue more acquisitions in Europe and possibly one in India, which would make it an even more serious player in the international long-haul market. At the same time, Etihad will have to prove in 2013 that its current investments are paying off. While Virgin Australia—which is also partly owned by Singapore Airlines and Air New Zealand—looks good, there are major questions about whether its riskiest investment, Air Berlin, can be turned around.

Vueling's impressive performance over the past few years could turn out to be a blessing and a curse. The airline is doing so well that International Airlines Group, which is already a shareholder, plans to fully acquire the carrier in 2013. The question is whether that will be a major advantage or impact the business model and reduce Vueling's ability to grow in its niche. Vueling has been one of the most creative low-cost carriers with CEO Alex Cruz at the helm, and it is going against traditional LCC behavior by opening up to connecting traffic and cooperating with legacy carriers. So far it all looks good, but major challenges are still ahead.

Only a year or so after the merger of Iberia and British Airways, the International Airlines Group (IAG) is already in crisis mode. This time, all attention is on Iberia, which has to implement a draconian cost-savings and capacity-reduction program. This will see the airline withdraw from essentially all European routes that are not needed as feeders for its long-haul network to Latin America. Iberia is also axing 20% of its workforce, and IAG says still more drastic plans are in the cupboard if agreements cannot be reached quickly with unions. As the examples of SAS Scandinavian Airlines and others show, unions have few options to oppose such restructuring moves in tough times.

Germanwings is taking over all Lufthansa short-haul flights except the feeder network into Frankfurt and Munich on Jan. 1. Lufthansa—Germanwings' parent—has finally concluded that it cannot operate short-haul flights profitably while competing against low-cost carriers. The move to allow Germanwings to grow has been long overdue, many observers believe, but internal group politics and concerns over brand dilution had kept Lufthansa from going ahead with it. Now, within a short space of time, Germanwings has to integrate 35 more narrowbody aircraft as well as cabin crew and pilots, and take over dozens of routes. In 2013, it will become clear how the transition is progressing.

Like Iberia and Lufthansa, the Air France part of the Air France-KLM group is in the midst of a major streamlining exercise that it expects will make it 20% more efficient. Putting its short-haul operation back on track is only one of the tasks that Air France has to address in 2013. Its bilateral alliance with Etihad Airways has to be implemented, along with new code-sharing arrangements with Air Berlin, both of which represent deals outside of the SkyTeam alliance. But of even more strategic importance, the group has to determine if it wants to grow further by taking a larger stake in Alitalia or investing in other subsidiaries.

With Andrew Compart, Christine Grimaldi, Darren Shannon and Madhu Unnikrishnan in Washington; Leithen Francis in Singapore; and Bradley Perrett in Beijing.