Analysis of the 1992–1996 period shows that every player in the air transport chain is far more profitable than the airlines, who collect and pass through fees and revenues to them from ticket sales. While airlines as a whole earned 6% return on capital employed (2–3.5% less than the cost of capital), airports earned 10%, catering companies 10–13%, handling companies 11–14%, aircraft lessors 15%, aircraft manufacturers 16%, and global distribution companies more than 30%. (Source: Spinetta, 2000, quoted in Doganis, 2002)
In the 1990s, "open skies" agreements became more common. These agreements take many of these regulatory powers from state governments and open up international routes to further competition. Open skies agreements have met some criticism, particularly within the European Union, whose airlines would be at a comparative disadvantage with the United States' because of cabotage restrictions.
To sum up: a lot depends on your own stamina because island hopping means packing and unpacking, getting on and off buses and ferries. Limit your choice of islands to perhaps one or two less than you think you can manage. Maximise transport links to avoid backtracking or port-transferring and since you are traveling high season be aware that you will usually need bookings ahead at most places. It is possible to turn up on an island and not find a place to stay or have to make do with a third-rate option.
Sarah-Jane — Thanks for another helpful article (this one on planning an island-hopping trip). Chasingthedonkey.com is a great website and my first go-to place for information on Croatia. I have scheduled my third 3-month-long stay and still have so much to do and see in Croatia. Personally, my favorite times to visit are in the “shoulder” seasons …. September-November and March-May.
I think that’s a great plan. Santorini is a must and Milos and Naxos are two islands that have both great beaches and lots to do and see away from the beach. Renting a car and exploring the interior villages of Naxos is a must-do and so is a boat tour around Milos. If you’re willing to cut Athens to 2 days, I would recommend Santorini 5 days, Milos 3 days, Naxos 3 days, and Athens 2 days.

Since airline reservation requests are often made by city-pair (such as "show me flights from Chicago to Düsseldorf"), an airline that can codeshare with another airline for a variety of routes might be able to be listed as indeed offering a Chicago–Düsseldorf flight. The passenger is advised however, that airline no. 1 operates the flight from say Chicago to Amsterdam, and airline no. 2 operates the continuing flight (on a different airplane, sometimes from another terminal) to Düsseldorf. Thus the primary rationale for code sharing is to expand one's service offerings in city-pair terms to increase sales. 
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