Sept 15 (Reuters) - U.S. natural gas prices for Monday

in the Permian shale basin in West Texas turned negative as

autumn pipeline maintenance and other constraints trap gas in

the nation's biggest oil-producing basin.

Financial company LSEG said that average gas output in the

Lower 48 states has dropped to 107.6 billion cubic feet per day

(bcfd) so far in September, down from a record monthly high of

108.3 bcfd in August.

Traders have noted the pipeline maintenance trapped some gas

in the Permian basin, helping spot gas prices at the Waha Hub

to fall by more than 2,350% from about 6 cents

per million British thermal units (mmBtu) for Friday to a

17-week low of minus $1.26 for Monday.

That was the sixth time Waha prices have averaged below zero

in 2025 and compares with an average of $1.66 per mmBtu in 2025,

77 cents in 2024 and $2.91 over the previous five years

(2019-2023).

Waha prices first averaged below zero in 2019. It happened

17 times in 2019, six times in 2020, once in 2023 and a record

49 times in 2024.

Analysts have said that negative prices were a sign the

Permian region needs more gas pipes.

There are some pipes under construction, including Kinder

Morgan's ( KMI ) Gulf Coast Express expansion, the WPC joint venture's

Blackcomb and Energy Transfer's ( ET ) Hugh Brinson, but they

are not expected to enter service until 2026.

The Permian in West Texas and eastern New Mexico is the

nation's biggest and fastest-growing oil-producing shale basin.

A lot of gas also comes out of the ground with that oil.

Even though U.S. crude futures are down about 12% so

far in 2025, energy companies have been willing to take some

losses on gas because they can still make up for those with

profits from selling oil.

But with oil prices on track to decline for a third year in

a row in 2025, some energy companies plan to reduce the amount

of capital they will spend on new oil drilling this year. Over

time, that could result in less oil and associated gas out of

the Permian.

Nationwide, U.S. oil and gas output is expected to reach

record highs in 2025 before easing in 2026, according to the

latest federal outlook.

(Reporting by Scott DiSavino

Editing by David Goodman

)