Bulgaria has become the second European country after France to ban exploratory drilling for shale gas using the extraction method called "fracking".
Bulgarian MPs voted overwhelmingly for a ban on Wednesday, following big street protests by environmentalists.
Bulgaria has revoked a shale gas permit granted to US energy giant Chevron.
Critics say shale gas drilling can poison underground water and even cause earth tremors. Industry experts say correct drilling is safe.
Hydraulic fracking involves releasing gas trapped in rocks by pumping in water mixed with sand and chemicals at high pressure. The technique is used widely in Canada and the US.
The Bulgarian drilling ban stipulates a fine of 100m levs (£43m; $66m) for any infringements.
Last Saturday protesters rallied in several Bulgarian cities urging the government to halt drilling for shale gas.
Currently Bulgaria and many of its former communist neighbours rely heavily on imported Russian gas.
Chevron had been given a permit to prospect for shale gas in northeastern Bulgaria.
In Poland, shale gas and oil are seen as promising alternatives to imports of Russian energy.
A new Polish geological report says there are indications of large shale oil deposits near Warsaw, Radom (south of Warsaw) and Elblag near the Baltic coast.
The Polish daily Dziennik Gazeta Prawna says estimates of Poland's shale gas resources will be presented in March.
Polish radio says US giant ExxonMobil is best placed to take advantage of the finds. ExxonMobil has been granted shale oil exploration licences in Poland.
But the radio says Chevron's plans to drill for shale gas in southeastern Poland have met with protests in the villages of Rogow and Zurawlow.
Last June, the French parliament imposed a ban on fracking, amid pressure from environmentalists.
But the French ban does not rule out other methods for recovering shale gas or oil.
In the UK, the energy firm Cuadrilla suspended test drilling for shale gas last year after a study linked it to earth tremors.
The study also said the tremors, near the northwestern resort town of Blackpool, were due to unusual rock formations at the well site.
Environmentalists have demanded a moratorium on fracking in the UK.