December 29, 2025 [Pipeline & Gas Journal]- Energy Transfer plans to increase the capacity of its proposed Transwestern Pipeline Desert Southwest expansion after strong customer demand emerged during a recent open season.

The project, which will move natural gas from the Permian Basin to markets in Arizona and New Mexico, will be upsized by increasing the mainline diameter from 42 inches to 48 inches. The change raises potential throughput to as much as 2.3 billion cubic feet per day, depending on final compression configuration.

Energy Transfer said demand growth in the Desert Southwest — including population growth and the potential retirement or conversion of coal-fired power plants — drove the decision to expand the project’s scope.

“Transwestern’s Desert Southwest pipeline expansion is an important critical source of natural gas,” said Ted Geisler, APS President and CEO. “We look forward to Energy Transfer enhancing this project to enable greater resources across the region.”

“Natural gas generation is an important part of SRP’s all-of-the-above approach to ensuring reliability and affordability for our customers,” said Bobby Olsen, SRP Associate General Manager and Chief Power System Executive. “The Transwestern Desert Southwest Pipeline expansion will help enable us to meet the region’s growing power needs and strengthen Arizona’s energy infrastructure.”

“We applaud the announcement of additional pipeline capacity along the Desert Southwest expansion project,” said Patrick Ledger, CEO of Arizona G&T Cooperatives. “This infrastructure is urgently needed to power the growth and business development taking place in rural Arizona.”

As a result of the upsizing, the project’s estimated cost has increased to about $5.6 billion, excluding allowance for funds used during construction. Energy Transfer said the change will raise its total growth capital spending in 2026 by roughly $200 million.

The company continues to target an in-service date in the fourth quarter of 2029.