I worked as a consulting architect with a young architectural firm
that recently won a large railroad complex project in a central
European country that was admitted last year to EU.
The city and the railroad company are in a proces of selecting a
forein real-estate developer that is to finance, build, and manage to
multipurpose project worth some $ 200 million. The selection of the
developer proceeded over the past few month in a "soft" manner with
many visits and discussions with possible investors-developers. In
the final selection are four large European firms, each with an extensive 
experience in building this type of mega projects.

Considering the rather informal manner of selection proces so far and the
facts that details of offers can not be easily compared in a
methodical manner I worry that once the selection is announced the
selected developer can start questioning different details of the
project itself, of the utilities, subsidies, time schedules, etc. and have at all
times a "way out" of the project and therefore also a possibility of 
blackmail.
The question:
1)What kind of a "performance bond" can be asked from the four
finalists before the selection is made?
2)Where can I find related documentation? 
The amount of cash required from the developer, to buy the land, could
be about  $ 30 million with the rest financed by banks.
3)What amount, or percentage of the cost of the total project, should
the requested performance bond therefor be?
4)What else should we worry about and look out for?

Greetings Tosop-ga
Congratulations on the architectural firm's winning the project.

"Considering the rather informal manner of selection proces so far..."

Contracts in the EU for such projects must be open to bidding throughout the EU.
There is nothing informal about this process, as these sites may suggest to you.

http://www.dti.gov.uk/about/procurement/procue8-8.htm

http://simap.eu.int/arch_old/european_pb_part1_en.html

I am absolutely no expert on this, just know from the newspapers that
on seemingly minor projects disputes arise because the proper
procedure was not observed.
Although it seems unlikely, perhaps the city and railway company in
the new EU member are not aware of this.

With all respect for the expertise of Google Answer Researchers, I
believe that you need advice from someone very experienced on the
subject.

G-A Researcher Lila-ga has shown an understanding of EU matters on
other questions.  Perhaps she can guide you to sources that will help
answer your questions.

Regards, Myoarin