The Big Burp

Sparking up tired oilfields

Carbon dioxide is a clear gas that puts the bubbles in pop and beer and makes drinkers burp. The fact that it can do as much for tired oil wells, and thereby rejuvenate them, has made CO2 one of the most promising ingredients in the U.S. energy mix. Indeed, oil firms are now sinking more than $1.5 billion into a pair of pipelines to deliver CO2 from southern Colorado to declining Texas oilfields, even though falling oil prices threaten to squeeze the ventures' profits.

The two efforts are the largest CO2 projects ever. In one, Exxon Corp. and Atlantic...