Most of the soldiers of fortune, who command fees of several thousands of dollars a day, are specialists in heavy weapons, helicopter technology and tactics, the EUobserver reported Tuesday.
Michel Koutouzis, a Greek expert on organized crime, said he found the majority of the mercenaries come from Belarus, Serbia and Ukraine.
However, the group includes a significant number of Polish helicopter experts and some Belgian, British, French and Greek nationals, he told the EUobserver.
In addition to the Europeans, Koutouzis said Gadhafi has hired much larger numbers of fighters from the Central African Republic, Chad, Niger, Mali and Somalia to battle rebel insurgents in Libya.
Koutouzis, whose French-based consulting company does research on security issues, spent February and March traveling in North Africa.
"In Libyan society, there is a taboo against killing people from your own tribal group," he said. "This is one reason Gadhafi needs foreign fighters."