Were the two companies to combine, they would overtake EQT Corp (EQT.N) as the largest natural gas-focused exploration and production company in the U.S. by market value, at a time when shale companies are seeking scale and efficiencies.
Southwestern's shares ended trading on Tuesday up 8.3% at $7.33 on the news, at their highest finish in almost a year. Chesapeake's shares closed up 0.7% at $89.59.
Chesapeake's talks with Southwestern are preliminary, with no certainty the two sides will reach a deal, the sources said. Chesapeake could explore other potential acquisitions, and may end up pursuing a different target, the sources added.