I want to find the best head hunters for hiring specialized people for
oil and gas exploration companies to work in Europe, Asia or Africa,
or in the US but providing sponsorship (I am a Spanish citizenship,
so I require sponsorship to be able to work in the USA). My focus is
in the reservoir engineering area.

Have you gone to the big operators? Shell, BP, Esso?
If you are looking for consulting, rather than direct hire, you'd most
likely get best results by talking directly to HR staff in countries
of interest and asking what body shop they use.
For example -- If you were looking into south east Asia I would say go
to Smedvig for subsurface skill set. European work might go via Deutag
or several operators out of Aberdeen. It isn't a global market type of
thing.

Best thing you can do is either contact the operators dorectly or
break out the rolodex and get in touch with anyone you might know or
have worked with/for. Talk to people you know and ask them about it.
Everyone has someone in their department that has had an experience
with headhunting or mature hire. Word of mouth is key though.

-RR

hi, i hope you'll find a job in oil and gas industry as me with this good tool:
http://www.applyoilandgasjob.com
the listing is not expensive and very complete... take a look...
michel