(Compares with estimates, adds background on Alberta production cuts)
March 7 (Reuters) - Canadian Natural Resources Ltd reported a surprise quarterly loss on Thursday because of lower crude prices, but said Canadian crude differentials have narrowed since Alberta imposed output curbs last year.
Alberta oil producers have endured record discounts on benchmark Canadian heavy crude because of congestion on export pipelines that led to a glut of crude building up in storage tanks.
That prompted the provincial government to impose temporary production cuts effective Jan. 1 to help clear the bottleneck, and announce plans to lease 4,400 rail cars to help move crude out of Alberta to higher-priced markets.
The company, which backed the Alberta government's move last year, said on Thursday that the Western Canadian Select differential index - the difference between benchmark Canadian heavy crude and U.S. crude - had narrowed to $12.38 a barrel in the first quarter of 2019 from $39.36 per barrel in the reported quarter.
For the fourth quarter, the company posted a loss when analysts were expecting a profit, as average realized prices of crude oil and natural gas liquids more than halved to C$25.95 per barrel.
Calgary-based Canadian Natural said daily output rose 6 percent to 1.08 million barrels of oil equivalent per day (boe/d) in the quarter.
Production beat analysts' average estimates of 1.07 million boe/d, according to IBES data from Refinitiv.
Net loss was C$776 million, or 64 Canadian cents per share, in the fourth quarter ended Dec. 31, compared to a profit of C$396 million, or 32 Canadian cents, a year earlier.
Adjusting for one-time items, the company posted a loss of 21 Canadian cents per share against expectations of a 14 Canadian cents profit. (Reporting by Debroop Roy in Bengaluru and Nia Williams in Calgary; Editing by Shailesh Kuber)