Croatia published an international tender for on-shore exploration for oil and gas in the Drava river basin and the east of the country, the Economy Ministry said on its website.
The tender, published in the official journal of the European Union on Friday, will run until Feb. 18 next year, it said. Licences for six separate blocks, covering an area of some 15,000 square kilometres, will be granted for up to 30 years.
Croatia is also running an international tender for off-shore exploration in the Adriatic, which is open until early November.
The former Yugoslav republic, which joined the European Union in July 2013, hopes that a drive to boost energy independence will help its economy recover. Croatia is expected to suffer a sixth recession in a row this year.
The head of Croatia's hydrocarbon agency, Barbara Doric, told Reuters last month that some 45 companies had applied to visit the data room for off-shore exploration.
Officials have declined to identify any interested firms, citing legal limitations, but local media said the potential bidders could include Gazprom and Lukoil from Russia, Exxon from the United States, France's Total and Germany's RWE.
Another round of on-shore concessions, for the Sava basin and northern Croatia, will be published in the autumn, followed by a subsequent round for the central Dinarides mountain chain in 2015, Doric said in last month's interview.
"Unlike off-shore exploration, in on-shore deals it is possible to have commercial production already after three years, because the exploration process is simpler," she said.
Croatia recently got a location permit that will allow a long delayed liquefied natural gas (LNG) terminal project in the northern Adriatic to move ahead. The project is one of several dozen EU energy projects the bloc may co-fund.
U.S. Assistant Secretary of State Victoria Nuland said last week Croatia could play a vital role in ensuring regional energy security by providing a source of supply for European countries and allowing them to reduce their dependence on Russian gas.
By Zoran Radosavljevic