As Congress debates legislation to slow global warming by limiting emissions, engineers are tinkering with ways to capture and store carbon dioxide, the leading heat-trapping gas.

But coal-fired power plants, commonly identified as the nation’s biggest emissions villain, may not be the best focus. Rather, engineers and policymakers say, it may be easier and less costly to capture the carbon dioxide at oil refineries, chemical plants, cement factories and ethanol plants, which emit a far purer stream of it than a coal smokestack does…

Lending momentum to this thinking, a Texas company, Denbury Resources, is building a 320-mile pipeline for carbon dioxide that will run from Louisiana to Houston.

Initially the pipeline will take natural underground deposits of carbon dioxide in Mississippi to the aging oil fields of east Texas, where it can be used to force more oil to the surface.

But as the pipeline threads its way through more and more refineries and plants — the chemical heartland of the United States — manmade carbon dioxide captured at those sites could also be added and stored.

Sequestering a ton of carbon dioxide from a chemical plant would have the same effect on the Earth’s atmosphere as storing a ton from a coal plant, scientists and industry executives emphasize.

“Sequestration is not a coal technology — it is a greenhouse gas abatement strategy,” said S. Julio Friedmann, leader of the carbon management program at Lawrence Livermore National Laboratory…

What oil drillers pay for carbon dioxide depends on the value of the oil it will help produce. When oil is at $70 a barrel, carbon dioxide goes for $10 or $11 a ton, said Tracy Evans, the chief executive of Denbury, the Texas company building the carbon dioxide pipeline.

Should the Congressional legislation mandate a cap-and-trade system, that modest price could be very important. “Wherever you can go to store a ton of carbon the most cheaply, you will go,” said Mr. Holmstead, the former E.P.A. administrator for air.

Not only applies reason to the questions of sequestration vs. source, it begins to make cap-and-trade sound sensible, viable.