In an analysis of air travel searches across the US, UK, Germany and France from June 2013, Searchmetrics has identified the most visible brands offering air travel tickets in both paid and organic search.
As far as methodology, the company explains:

Searchmetrics analyzed which sites rank in the top 15 positions in Google’s organic and paid search results for a list of the 1,439 most popular search terms related to “flights” in US and UK English and French and German.
The study analyses the most visible websites providing air travel across Google.com’s paid and organic search results, where visibility is defined by Searchmetrics’ ‘Paid Visibility’ and ‘SEO Visibility’ scores.
For this analysis it calculated the ‘Paid Visibility’ and ‘SEO Visibility’ scores based on:
The number of times a domain appears in the search engine results pages (SERPs) across the keyword set related to FlightsIts prominence within those SERPs (a higher ranking equates to a higher visibility score)The competitiveness of the keyword (higher search volumes equate to a higher visibility score)
The company also gently reminds readers that these results are only indicators of visibility from a website's organic and paid search channels - not a wider representation of website traffic or other metrics.
United States
In the United States, Expedia dominates, with a visibility ranking of 51,401. Kayak follows relatively close behind, with CheapFlights.com, Travelocity, and Orbitz rounding out the top five.
As far as paid search results in the US, it gets interesting as the lineup shifts. Cheapoair, Orbitz, OneTravel, Kayak and Southwest.com are the most prolific paid advertisers.
The #1 organic result, Expedia, does not even appear on the list of those spending the most on paid visibility.
Given the success of Expedia's extensive "Find Yours" campaign, both in earned and paid media across multiple platforms (including television), it's likely that the company simply has refocused dollars to fuel an organic approach - an approach that appears to be working, according to this analysis.
There's also the factor of increased brand loyalty - for companies that derive a significant share of revenues from repeat customers, the value lies in increasing the customer's lifetime spend. This means that customers will likely come into the funnel via e-mail advertising or by directly visiting the brand.com website.
In fact, the study looked at Social Visibility as well. This offers some more clear insight into the impact of brand-building efforts of air travel ticket sellers today.
The results here show how a focus on search optimization can translate into organic SEO visibility. This is perhaps related to the need for a constant stream of original content for social media - which just happens to be effective fodder for search engines.
One of the outliers here is Cheapflights, which has a high organic SEO visibility unmatched by a significant presence on social media in the US. Delta also has apparently committed more resources to a much more visible presence on social, rather than spending extensively on paid and organic SEO. Or perhaps their existing efforts in those arenas are simply eclipsed by the success managed on their social channels.
UK, France and Germany
The European results yield a considerably different crop, demonstrating different priorities across the pond from air travel sellers in the United States.
In comparison with the US market, where the airlines are still maintaining some direct presence with consumers, airlines working in the French market have basically given up market share to the travel comparison sites. In fact, only Air France shows up in the organic SEO visibility rankings.
In addition, airlines don't have access to as large a swath as inventory as competing travel comparison sites.
This means that there is simply not as much for search engines to index, and fewer opportunities to rank. So while the loss of position as far as SEO visibility of airlines in European markets may indicate the reduced reliance on traditional SEO techniques, it may also simply point to the realities of each company's product.
Germany shows much of the same characteristics of France.
The UK, however, shows that travel portals are seen as a significant distribution channel for the airlines. The top travel portals are succeeding in their SEO efforts, and absolutely dominating the space.
Airlines have either ceded to the travel portals by reducing investment in SEO, or have allowed those portals to do what they excel at while leaving their own airlines to the areas they do best.
All of this is turned on its head a bit when considering the Paid Visibility across these countries. Many of the same brands dominant in their SEO commitments don't implement a paid match.
In the UK results, Skyscanner is the primary example of this.
Germany and France also see the travel portals spend significantly more than airlines in their efforts to bring travel shoppers into their sales funnels.
The full study looks at backlinks and specific keyword optimizations, and can be downloaded here.
NB: Chess image courtesy Shutterstock.