HOUSTON, Jan 26 (Reuters) - Grades were mixed on Monday, dealers said, as investors weighed a drop in production alongside a decline in refinery demand after winter storms hit the U.S. energy sector over the weekend.

U.S. oil production outages peaked on Saturday at 2 million barrels per day, or up to 15% of the country's production, consultancy Energy Aspects estimated, with the Permian Basin likely to have experienced the largest share of that decline at around 1.5 million bpd.

Production losses eased on Monday, with Permian shut-ins estimated at about 700,000 bpd and production set to be fully restored by January 30.

North Dakota crude output, meanwhile, is currently down by between 80,000 bpd and 110,000 bpd, as operators shut production in due to cold weather, the state regulator said on Monday.

Cenovus Energy's 172,000-barrel-per-day Lima, Ohio, refinery experienced mechanical issues caused by a major winter storm that hit much of the United States over the weekend, industry monitor IIR Energy said.

Calumet Specialty Products' Shreveport, Louisiana, refinery, with a capacity of 60,000 barrels per day, suffered from winter storm-related issues, IIR said on Monday. REF/OUT

• Light Louisiana Sweet for March delivery was steady at a midpoint of a $1.23 premium and was seen bid and offered between a 95-cent and $1.50 a barrel premium to U.S. crude futures CLc1 ​

• Mars Sour rose 20 cents to a midpoint of a $1.80 discount and was seen bid and offered between a $1.90 and $1.70 a barrel discount to U.S. crude futures CLc1 ​

• WTI Midland fell 35 cents to a midpoint of a 65-cent premium and was seen bid and offered between a 55-cent and 75-cent a barrel premium to U.S. crude futures CLc1 ​

• West Texas Sour fell 25 cents to a midpoint of a $2.85 discount and was seen bid and offered between a $2.95 and $2.75 a barrel discount to U.S. crude futures CLc1 ​

• WTI at East Houston , also known as MEH, traded between a 85-cent and $1.05 a barrel premium to U.S. crude futures CLc1 ​

• ICE Brent March futures LCOc1 fell 29 cents to settle at $65.59 a barrel

• WTI March crude CLc1 futures fell 44 cents to settle at $60.63 a barrel

• The Brent/WTI spread widened 12 cents to last trade at minus $4.93, after hitting a high of minus $4.75 and a low of minus $4.95

(Reporting by Georgina McCartney in Houston; Editing by Jamie Freed)

((georgina.mccartney@tr.com))