Croatia on Wednesday launched a tender for licenses to explore and drill for potential oil and gas reserves in the Adriatic, hoping to attract investments badly needed for its ailing economy.

Representatives of more than 40 firms, including Russia's Gazprom and US oil giant ExxonMobil, attended a presentation of the 29 exploration blocks ranging between 1,000 and 1,600 square kilometres (386 to 617 square miles) that are being tendered.

Bidding is to close on November 3 while exploration is to last up to five years.

According to previous estimates, exploration could generate some $2.5 billion (1.8 billion euros) in business for the new EU member, whose economy is expected to stagnate in 2014 after five years of recession.

"A succesful tender will make Croatia a key gas and oil provider in this part of Europe and our gas will be the cheapest in the region," said Economy Minister Ivan Vrdoljak at a conference presenting the tender.

He cited good oil and gas infrastructure including the Adriatic pipeline system JANAF, access to a network of refineries in the region as well as ports and shipyards alongside the coast as Croatia's main advantages for investors.

The tender was launched after a five-month preliminary geological survey conducted by Norway's Spectrum ASA seismic data provider was completed in January.

No environmental impact study was conducted, but the economy ministry said firms conducting drilling would need to comply with strict environmental safety regulations.

Environmental groups, which are seeking a public debate, have warned that the offshore drilling could have a negative impact on tourism, which is based mostly on Croatia's stunning coast with more than 1,000 islands and islets.

The tourism sector has developed into a key part of the former Yugoslav republic's economy since it gained independence in 1991.