Exploration company Petroceltic International said it sold its Romanian unit to GVC Investment as it exits high-risk exploration ventures.
Petroceltic also withdrew from Iraqi Kurdistan in March.
It said it bought out the stakes of its partners Sterling Resources and Beach Energy in the Romanian fields before the sale to GVC.
Financial details of the transactions were not disclosed.
Brian O'Cathain, CEO of Petroceltic, said the deal now concludes the company's involvement in the Romanian Black Sea.
"This process of disengagement forms part of our strategy to focus our efforts on our production and development assets, and to exit from high risk exploration ventures. We have now withdrawn from Romania and Kurdistan, and are focusing our future exploration efforts on Egypt and Italy," he added.