NEW YORK - Cash crude differentials mostly firmed for a second day on Thursday on renewed refinery buying, but pared gains late in trade as the discount narrowed for prompt crude on futures markets.

Mars sour MRS- dealt for as little as $1.45 a barrel below West Texas Intermediate CLC1, but traded for -$1.85 later, down from levels of -$1.70 yesterday.

Light Louisiana Sweet LLS- firmed to $2.15 a barrel above WTI, up from +$1.80 on Wednesday.

Buyers were active in bidding for cash crudes after October cash grades started dominating trading on Wednesday, one buyer said.

U.S. crude futures rose, after falling earlier in the day, gaining $1.21 a barrel to $72.64 after settlement. Brent crude LCOV9 fell $1.02 to $72.67. Brent traded at a 3 cent per barrel premium to WTI. A premium for Brent helps to protect U.S. cash grades from more competition against imports.

WTI for October delivery was priced at 63 cents a barrel below WTI for November delivery, narrowing a contango discount that stood at 79 cents a barrel on Wednesday. The spread earlier had widened to as much as 88 cents, helping to firm cash grades.

Among other grades, Eugene Island crude EUI- traded for 20 cents a barrel below WTI. Its last publicly disclosed trade was at -20 cents a barrel on July 21. Poseidon sour PSD- traded for -$1.65 a barrel, up from -$1.75 on Wednesday. West Texas Sour WTS- traded for -$1.80, up from -$1.95.

On the West Coast, Alaska North Slope crude oil ASW- for October delivery last sold Monday for 40 cents a barrel over West Texas Intermediate, up 75 cents, traders said.

California buyers raised posted prices by $1.05 cents a barrel.

See  for Reuters' generic refining margins

See CL-1=R for the WTI front/second month spread

See CL-LCO1=R for front month WTI/Brent futures spread

See BFO- for Reuters' assessment of Dated Brent

See <0#FRT-> for Reuters assessed tanker rates

See BRNV for assessed domestic crude differentials

See PPGR for outright U.S. cash crude prices

See [REF/US] for a list of U.S. refinery outages
See [EIA/S] for U.S. EIA inventory reports and forecasts

See [CRU/TU] for recent cash crude deals
(Reporting by Joshua Schneyer; Editing by David Gregorio)