In addition to the well-known gas shale plays like the Barnett, Haynesville, Marcellus, and Eagle Ford, and oil plays like the Bakken, there are perhaps dozens of smaller, less well-known resource plays, many of which are in the very early stages of exploration and development. Some of the plays are shale and others are tight gas or coalbed methane. Many are in the United States and Canada, but increasingly exploration and production companies are using modern drilling and production technology to develop natural gas and oil from unconventional subsurface formations in Europe and Asia. Doubtless, unconventional resources eventually will be exploited in Africa, South America, and Australia as well. What we call “unconventional” today will be considered “conventional” in time.