Unconventional resources of crude oil and natural gas – shale energy – increased significantly in the US in the early 2000s, triggered by the strong rise in the price of crude oil and technical advances in production. The US is a clear forerunner in the production of shale energy, due to its existing knowledge and infrastructure. The rest of the world is following, although negative environmental effects and other factors have obstructed the diffusion of new extraction methods. In Europe, Polish production is expected to start in the next few years, although environmental concerns are delaying the onset. The rise in the importance of shale energy will increase global oil and gas production markedly. The rising global supplies will improve global energy security in the long run and help to stabilise the large international price differences for natural gas.