Dec 17 (Reuters) - Mars Sour strengthened to its highest level in more than eight months on Tuesday, dealers said, due to a lack of sellers for the grade in the market.

Mars firmed 90 cents to a premium of $2.10, its highest since April 1, when plans by Mexico's state-controlled oil company to halt some crude exports pushed prices of the offshore crude higher.

Mars has been trending higher in recent days, also helped by strong refinery demand, as processing units ramp up after fall maintenance.

Meanwhile, the spread between U.S. West Texas Intermediate and Brent crude narrowed to its least in nearly three months. It eased for a third straight session to as little as minus $3.50 per barrel.

A narrower spread between the global benchmark and WTI, particularly under minus $4, typically discourages transatlantic demand.

In refining news, HF Sinclair DINO.O said on Monday it had extinguished a fire at its Holly Frontier refinery in Tulsa, Oklahoma, according to local media.

On the supply side, U.S. crude oil stocks fell by 4.69 million barrels in the week ended Dec. 13, market sources said, citing American Petroleum Institute figures on Tuesday. That compared with estimates for a draw of 1.64 million barrels, according to a Reuters poll.

* Light Louisiana Sweet WTC-LLS for January delivery eased 8 cents to a midpoint of a $2.95 premium and was seen bid and offered between a $2.75 and $3.15 a barrel premium to U.S. crude futures CLc1

* Mars Sour WTC-MRS firmed 90 cents at a midpoint of a $2.1 premium and was seen bid and offered between a $1.90 and $2.3 a barrel premium to U.S. crude futures CLc1

* WTI Midland WTC-WTM strengthened 5 cents to a midpoint of a 75-cent premium and was seen bid and offered between a 50-cent and $1.00 a barrel premium to U.S. crude futures CLc1

* West Texas Sour WTC-WTS was unchanged at a midpoint of a 45-cent discount and was seen bid and offered between a 55-cent and 35-cent a barrel discount to U.S. crude futures CLc1

* WTI at East Houston WTC-MEH, also known as MEH, traded between a $1.00 and $1.40 a barrel premium to U.S. crude futures CLc1

* ICE Brent February futures LCOc1 fell 72 cents to settle at $73.19 a barrel on Tuesday.

* WTI January crude CLc1 futures fell 63 cents to settle at $70.08 a barrel on Tuesday.

* The Brent/WTI spread WTCLc1-LCOc1 narrowed 12 cents to last trade at minus $3.50, after hitting a high of minus $3.50 and a low of minus $3.69.

(Reporting by Arathy Somasekhar in Houston; Editing by Matthew Lewis)

((Arathy.s@tr.com))