Economic Minister Ivan Vrdoljak opened the auction Wednesday for 29 blocks covering an estimated 600 square miles.
The country meets more than half of its annual gas demands through domestic resources, but aims to add a layer of security to its energy sector with more oil and gas discoveries.
As of January 2013, the country has proved crude oil reserves of around 71 million barrels and proved gas reserves of 880 billion cubic feet.
Fifty companies last month expressed interest in acquiring seismic data that would give them a better understanding of the oil and gas potential in the Croatian waters of the Adriatic Sea.
The auction closes in November and the government is expected to award contracts by March 2015.