Third of five episodes. The Planet Money oil faces a test, we sell it, and we meet the man who set off the fracking boom in America.

Crude prices have been at three-year lows this week as the world appears to be awash with supplies. With OPEC apparently not willing to defend higher prices by reducing their output, attention has turned to the likely impact on U.S. shale production of a lower price regime. Today we explore why shale production is unlikely to slow down rapidly and may even increase as producers move rigs to plays with higher returns.