Last month, private equity firms Cinven Ltd. and BC Partners Ltd. cashed out of their remaining investment in travel technology and distribution company Amadeus IT Group SA. The €385.8 million ($529 million) sale is just the latest step in a financial round robin that saw the two European private equity firms, along with airlines Air France-KLM, Iberia Líneas Aéreas de España SA and Lufthansa AG, buy the Madrid-based global distribution system, or GDS, in July 2005 for €4.34 billion in a mammoth take-private deal. The partners then acquired a number of companies to broaden Amadeus' capabilities, suffered through some tough years and relisted shares in an April 2010 initial public offering in Spain.

The Oct. 19 sale of a 6.842% stake was at a slight discount to the price of shares trading before the deal, but gave Amadeus a €5.64 billion market capitalization and a hefty return for the sellers.

That transaction and the tortuous path to get there aptly demonstrate the unsettled nature of the travel industry that Amadeus supports.

By most reckonings the world's largest industry, global travel and tourism this year should eclipse $900 billion, according to estimates by travel industry research concern PhoCusWright. This is a vast, diverse enterprise, propelled by necessity and desire, but buffeted, in the past year alone, by everything from uppity Icelandic volcanoes to Hurricane Irene and walloped by Greek sovereign debt, Egyptian protesters and American unemployment rates. It's a bumpy ride at the best of times.

Turbulence jolts as well market intermediaries, which in the old days used to be called travel agencies. Advanced search engines, mobile phone apps and social media recommendation sites all conspire to disrupt the old order and the older new order in how trips are booked, where people stay and what they do once they get there. "The industry goes through evolutionary cycles, then significant mutations that leapfrog the industry forward," says Mike Kistner, president, CEO and chairman of Dallas-based Pegasus Solutions Inc., a travel-related technology provider. Kistner talks of major shifts every 20 years or so. "Where we are today is another mutation," he says, adding quickly: "We feel [Pegasus] is part of that mutation."

Travel industry-related mergers, acquisitions, investments and divestments reflect all these crosscurrents. They provide both a proxy for what's going on in the industry and an active marketplace themselves.

Today's deal scene may not resemble the boom times of 2005 to 2007, when billion-dollar acquisitions such as Amadeus were commonplace and private equity poured money into the sector as if every plane ticket booked was a lotto winner. However, it's regained momentum from the post-financial crisis doldrums.

"There's a lot of pent-up demand. There weren't a lot of deals in 2008, 2009, 2010," says Frank Sena, New York-based managing director of Bentley Associates LP, a boutique investment bank focused on travel. "2011 is busier."

That's in large part a function of the industry itself, which is once again moving at a nice clip. According to PhoCusWright, the overall travel market grew last year at 7%, after a 10% decline in 2009. The research outfit estimates global travel will grow 6% this year.

The sector is being led by business travel. In the latest figures available, business travel grew more than 10% in August 2011 over 2010, according to estimates by Pegasus, which helps process some 6 billion transactions a month. "Even small agencies are doing really well," says Sena. "Most are doing well because people are traveling again."

Intermediaries themselves can generally be divided into two parts: offline, or traditional travel agencies, and online travel agencies. Add to those two more interlinked categories: distributors of travel and hospitality-related offerings, either to agencies or directly to consumers, and the technology that powers them. They can be as broad-based as Amadeus or as specialized as Hays Travel Ltd.'s Bonvoyage.co.uk website, which launched in August and offers online bookings for cruises, one of the last bastions of offline leisure travel.

The deal marketplace breaks down along similar lines. Valuations reflect a wide universe. "Multiples are all over the map," says Sena. A technology play, he continues, could garner Ebitda in the upper teens if the target has any earnings at all. "Even within traditional travel agencies, you'll see Ebitda range from 2 to 8 times," he says.

Consolidation remains the name of the game for traditional agencies. Larger agencies are buying smaller ones, many of whose owners are reaching retirement age and who lack the capital or inclination to invest in technology necessary to keep them afloat. "It's still a very mom-and-pop industry," says Sena, who believes that while "in 10 years there will still be thousands of travel agencies, eventually the smaller ones will disappear."

They're not exactly an endangered species, at least not yet. "We have a database of 9,000 travel and tourism companies owners," says Bob Sweeney, president of specialized brokerage Innovative Travel Acquisitions Inc. Sweeney says he brokers about two travel agency deals a month, with enterprise values from $600,000 to $10 million. In 20 years of business, he figures he's completed more than 500 transactions.

Major consolidators themselves have been joining forces, although most deals these days are smaller add-ons rather than the megamergers of the mid-2000s. In December 2010, for example, Flight Centre Ltd., Australia's largest agency and one of the biggest agencies in the world, paid $10.5 million for a 74% stake in Boston-based Garber's Travel Service Inc. (Flight Centre had bought 26% of the agency in 2007.) Flight Centre is adding Garber's to its U.S. holdings, garnered through the 2007 acquisition of Liberty Travel for $135 million.

Leisure travel usually boils down to getting the cheapest price, a function tailor-made for an online search. Corporate travel, by contrast, melds cost optimization with other factors such as service, policy compliance and demand management. That's where the money is for travel agencies. Customers pay fees. Suppliers, including even the notoriously stingy airlines, pay commissions.

New York-based American Express Travel; Carlson Wagonlit Travel, with corporate headquarters in Paris; and Utrecht, Netherlands-based BCD Travel BV are market leaders. According to Business Travel News statistics, Britain's Hogg Robinson Group is a distant fourth. All four have global reach and are the result of multiple mergers, expanding by buying strong players in various markets around the world. That quest for dominance continues. The latest deal occurred in October, when Carlson Wagonlit bought the Centenial Group in Costa Rica for an undisclosed amount.

To get a sense of scale, American Express and BCD each notched more than $17 billion in travel-related revenue last year. Travel commissions for American Express in 2010 amounted to $1.8 billion. Carlson Wagonlit, which combines revenue from its own operations and joint ventures, says total sales last year eclipsed $24 billion.

A few other players are trying to roll up agencies as well. Private equity firm Silver Oak Services Partners LLC, for example, bought for an undisclosed amount corporate travel management company Directravel in September and says it's in the market for more acquisitions as add-ons. Directravel is now headed by Ed Adams, who built up Navigant International Inc., which was sold to Carlson Wagonlit for $510 million in 2006.

"There are four leading players [in corporate travel] and then it's fragmented," says Daniel Gill, Silver Oak's managing partner. He describes corporate travel as a "high recurring revenue business" that rarely experiences a down year and grows at a respectable 4% to 6% annually.

That kind of sustained growth and relative predictability contrasts dramatically with the online universe, which is at once expanding at a rapid rate, colliding and cooling.

Travel is "perfectly suited to e-commerce, [where] decisions are based not only on price but on subjective information," says Alan Josephs, CEO and president of Perfect Escapes, an online site that focuses on luxury hotels and resorts. "The next generation of [websites] will be wiser, more targeted, have much more complete information, all making for a better online-booking experience."

Supermarket-style agencies dominate the broadest expanses of online travel, although they move with different velocity and trajectories. In an August review of the industry, CreditSights contrasted the fortunes of publicly traded competitors Priceline.com Inc., Expedia Inc. and Orbitz Worldwide Inc. In the second quarter of this year, Priceline.com revenue grew 44%, Expedia 23% and Orbitz just 4%. As CreditSights emphasized, the Priceline operation, which includes a deep discount option, dominates the far more lucrative and higher-growth online hotel bookings. Priceline's hotel bookings grew 56% in the second quarter. Orbitz's hotel bookings, by contrast, actually declined 1%.

The fourth online travel supermarket is Travelocity LLC, wholly owned by Sabre Holdings Corp. since 2002, when Sabre paid $420 million for the 30% stake it didn't own. Revenue isn't public, although estimates put Travelocity behind market leader Expedia and runner-up Priceline.com but ahead of Orbitz. Travelocity experienced a 28% decline in the 12 months through July, according to an industry report compiled by Barclays Capital in August.

Coming up fast is Kayak Inc., a site that aggregates and filters other online travel offerings.

More specialist online offerings continue to proliferate, and capital has followed. That's especially true for accommodation-related sites. As the Barclays study emphasizes, the hotel market is highly fragmented -- the travel-related social media reviews site TripAdvisor Inc. lists almost 500,000 properties around the world -- contracts are usually negotiated one hotel at a time, and the percentage of online bookings have lagged far behind air travel. Just about every major player in online travel is committing significant resources to gain an edge.

"Hotels are where the money is in the game," says Tim Mullaney, a PhoCusWright financial analyst, who notes that both Orbitz and Travelocity were "really late" ramping up hotel booking engines and offerings and have suffered for their lapse.

New lodging-related sites emerge all the time. This year, for example, Swedish venture capital firm Investment AB Kinnevik and German counterpart Rocket Internet GmbH invested $90 million in Wimdu GmbH, whose website books private accommodations for short-time visitors. Berlin-based Wimdu is ramping up quickly, according to Russell Goldman, a Wimdu co-founder, who heads U.S. operations. Wimdu, which emphasizes live-person customer service as well as savvy technology, has hired more than 400 employees and established offices in 15 countries since the company was founded in March.

"People don't plan vacations the way they used to," Goldman says, citing among other factors a growing reliance on social media for recommendations and guidance. Goldman maintains that because the travel sector has been slow to understand this, startups such as his have the ability to rapidly capture market share.

HomeAway Inc. is the pioneer and market leader in vacation rentals. Founded in 2005, the Austin, Texas-based company went public in June in a successful $216 million IPO that got the industry and investors alike salivating. While the share price has jumped around since, it remains far above the $27 offered in the IPO. Its market cap is close to $3 billion.

In the weeks before going public, HomeAway acquired two similar but smaller operations that provide Web-based vacation rental listings, one in Australia, the other in the U.S., for a total of $5.1 million. The company is open about using acquisitions as a means of expanding markets and powering growth.

Layer onto travel services technologies that run both on- and offline operations. Acquisitions abound, although most these days are small, low-profile purchases with no delineation of financial details. On Oct. 17, for example, Pegasus said it had acquired Open Hospitality, which provides online-marketing and -booking options for hotels. The two didn't announce terms.

Private equity firm Prides Capital Partners LLC bought Pegasus in 2006 for approximately $275 million.

Privately held Traina Cos., a New York-based real estate and hospitality group, offers another example. In May, Traina acquired Hickory Travel Systems Inc., which books $2 billion in sales annually, in part through a technology that allows business travelers to negotiate corporate hotel rates. Financial details weren't disclosed.

An emphasis on technology is understandable. Consumers and providers alike demand easier-to-use, more complete and more sophisticated offerings. In many cases, it's catch-up compared with other tech-savvy industries. "The travel sector is an innovation laggard," says Goldman. "Only recently has it been rapidly changing."

Attention in recent months has been especially focused on travel analytics concern ITA Software Inc., which Google Inc. announced in July 2010 it would acquire for $700 million. ITA technology compares airline fares and availability. Many online agencies vigorously opposed the acquisition, claiming Google, with its overwhelming dominance in online searches, will crowd out competitors. In April the Department of Justice signed off on the deal.

"That was the most significant transaction in quite a while," says Sena.

Among those most vocal in opposition to the deal was Kayak, which relies on the ITA software for much of its offerings. Kayak filed to go public a year ago but has repeatedly delayed its initial public offering and indicated in Securities and Exchange Commission filings the chances of an IPO are now reduced to 50%.

The online-offline world is blurring. Expedia developed its own corporate travel division, now called Egencia, and has expanded through acquisitions. The latest came in April when it acquired Travelforce, with operations in Australia and New Zealand. BCD, by contrast, has fashioned through acquisitions an online leisure division it calls Travix. The latest deal came in August, when Travix acquired hotel-booking site EasyToBook for an undisclosed price.

That kind of melding is understandable. Corporate-focused travel agencies book anywhere between 25% and 50% of their business online, according to various estimates. Some have developed their own technology platforms, and others rely on third-party technology vendors.

Like travel itself, travel industry-related M&A reflects a global marketplace. In Brazil, for example, Latin America's largest travel agency, CVC Brasil Operadora e Agencia de Viagens SA, has filed for an IPO. Carlyle Group paid an undisclosed amount for a 63.6% stake in the agency in early 2010 and looks to make a quick return.

Rival PE giant Blackstone Group LP hasn't fared nearly so well in its travel-related ventures. Along with Technology Crossover Ventures, which holds a minority interest, Blackstone bought the travel consortium Travelport Ltd. in a blockbuster 2006 deal for $4.3 billion from Cendant Corp. One Equity Partners LLC, the J.P. Morgan Chase & Co. private equity arm, acquired a minority stake later that year. Travelport spun out the consumer online agency Orbitz in an IPO a year later.

Through its Galileo and Worldspan subsidiaries, Travelport makes money primarily as a GDS, along with Amadeus and Sabre Holdings, one of three competing large engines that travel agencies traditionally use to connect with hotels and airlines for bookings. Like many of the airlines they link to, GDSs struggle with huge legacy systems. Built until recently on mainframe computers, these booking systems have been forced to invest heavily to provide needed technology and relevancy to travel agency customers. In June, for example, Sabre Holdings acquired at an undisclosed price SoftHotel, which provides online hotel pricing and inventory management systems.

Being saddled with a huge mountain of debt certainly didn't help Travelport in its efforts. Earlier this fall, Blackstone, Technology Crossover and One Equity successfully scrambled to refinance $715 million worth of Travelport pay-in-kind notes coming due in March and avoid bankruptcy. And the troubles don't end there. Blackstone and its partners still own 56% of Orbitz through Travelport. Orbitz is losing money, market share and market cap.

Accommodations-related sites are attracting some of the most spirited investor interest. Over the past decade, airlines have cut commissions to almost nothing. Airline booking is straightforward and established, with competition primarily between the major online sites and the airlines' own websites.

Hotels, by contrast, remain wide open, in terms of both brands and the way they are marketed. "It's still very fragmented," says Sena, which he says translates into much bigger commissions for booking agents. Contracts are still negotiated property by property, even among some of the bigger chains. Many of the independent hotels, especially in Europe and Asia, are only now contracting online associations. Agents "would rather sell hotels than air any day," Sena says.

Social media is playing a big role as well. With its readers-based approach to rating accommodations, destinations and restaurants, TripAdvisor is far and away the market leader. It boasts more than 50 million reviews. Owner Expedia announced in July that it would spin out TripAdvisor in an IPO, anticipated by year's end.

Some traditional agencies are making tentative forays into the world of social media. A year back, for example, Flight Centre acquired a majority stake in travel-related social network Gapyear Co. Ltd., which targets students and backpackers. It was a modest investment: £800,000 ($1.26 million).

While the days of multibillion-dollar buyouts may be over, the jockeying for both market share and positioning within the industry shows no signs of ending. Call it a reordering.

Amadeus is again instructive. Earlier this year, the company sold its online travel service, Opodo Ltd., for €450 million to a consortium of AXA Private Equity and Permira, which then merged the agency into two online agencies, eDreams, acquired in 2010 by Permira, and Go Voyages SA, bought about the same time by AXA. The new company is valued at more than €1 billion and ranks as one of Europe's largest online agencies.

Nine European airlines founded Opodo in 2000. Amadeus gained a controlling stake after it invested €62 million in 2004, acquired other smaller online agencies in France and Scandinavia the following year, then bought out airline partners in 2008 and 2009.

Wholly owned isn't wholly loved, however. Last year, Amadeus announced Opodo was no longer a strategic asset and put it up for sale. That's the way it goes in the travel business. Here today, gone tomorrow.