Economy ministers and state secretaries of the five countries voiced their "support for the enhancement of cooperation between the countries of the Pan-European pipeline (PEOP) route and those other countries that have expressed their interest in the PEOP project," a declaration signed here said.
EU leaders have become increasingly concerned at their dependence on Russia for energy imports, particularly natural gas, and are keen to increase their supply routes and diversify suppliers.
The 27-member bloc has also backed the construction of the Nabucco pipeline, which would carry gas from the Middle East and Central Asia to the EU, via Turkey and the Balkans.
Croat Prime Minister Ivo Sanader said the pipeline, which will have capacity to transport 80-100 million tonnes of crude oil annually, would cost 2.0-3.5 billion dollars (1.5-2.6 billion euros).
"This project providing for the transport of oil from ... the Black Sea to European market is a strategic project for both Croatia and all the countries through which it (the pipeline) will go," Ivo Sanader said.
"Today we made the first important step ... We believe that we will soon start with realization of the project," Sanader said.
European Union Energy Commissioner Andris Piebalgs, who co-signed the declaration, stressed the EU's support for the project, proposed back in 2002.
"I and my colleagues will do everything possible to facilitate the work ... (to) see implementation of this project," he stressed.
Piebalgs said that the Caspian Sea region would be supplying more and more to the world market.
"But to be really ready to accomodate the oil we need infrastructure plans and this infrastructure should be sound and avoid congestion that could provoke huge environmental damage if something goes wrong," he added.
"The Pan-European oil pipeline actually very much corresponds to this criteria."
The participating countries also stressed in their declaration that they would "consider what adjustments are justified to routing proposals in order to accomodate legitimate concerns relating to protected natural environments."
Environment protection played an important role in preliminary talks as Slovenia initially refused to join the project citing ecological concerns.
The declaration was signed on the sidelines of a one-day meeting on energy security, potential and investment in south-eastern Europe.
In Budapest on Tuesday, the head of the International Energy Agency also highlighted the importance of southeast European countries in diversifying EU energy supplies.
IEA chief Claude Mandil said that a planned liquefied natural gas terminal on Croatia's Adriatic coast would better help diversify Europe's energy sources than rival EU- or Russian-backed plans.
The terminal, which is currently planned in Croatia, could receive tankers from around the world and would transport gas via pipelines to central and western Europe. The location of the future terminal is currently being decided on, and the government has suggested it could be on the southern part of the coast, close to the border with Bosnia.
Russia meanwhile is pushing to extend its existing Blue Stream pipeline, which would carry gas along much the same route as Nabucco.
