American energy companies have spent billions of dollars in the past decade exploring for natural gas. But in parts of Texas and New Mexico, there is now so much of it that it is sometimes worthless. Some companies have even had to pay buyers to take it away.

Shale drillers in the Permian Basin are producing vast amounts of gas as a byproduct of prospecting for oil US:CLG9 . But there aren’t enough pipelines to take all the gas to market, causing some of it to become landlocked, and sending local prices into free fall.