(Adds states and shale basin cuts)
March 27 (Reuters) - The number of rigs drilling for oil in the United States declined by 12 this week to 813, the smallest decline since December, oil services firm Baker Hughes said in its closely watched survey on Friday.
That compares with declines of 41 and 56 rigs in the prior two weeks and is a sign the collapse in drilling over the past few months has slowed.
With the decline this week, the number of oil rigs has fallen for a record 16th week in a row to the lowest level since 2011, according to Baker Hughes data going back to 1987.
Despite the reduction in oil-directed rigs by about 49 percent since hitting a record high of 1,609 in October, the more than 50 percent decline in oil prices since the summer have forced U.S. energy firms to slash spending and idle wells but have not yet slowed oil output.
U.S. oil production hit 9.4 million barrels per day (bpd)last week, the highest since the early 1970s, according to the U.S. government data, as drillers focus on their most productive acreage, become more efficient at extracting oil from existing wells and complete previously drilled wells.
U.S. crude futures this week rebounded to over $50 a barrel this week from a six-year low near $42 last week on worries oil supplies from the Middle East could be disrupted due to the Saudi Arabia-led air strikes in Yemen. But by Friday, worries over Middle East disruptions eased and prices were down about 3 percent.
"At wellhead prices of $40 a barrel or less, half of incremental production is still profitable," analysts at Bank of America Merrill Lynch said in a report.
The bank anticipates the U.S. oil rig count will continue to decrease in the second quarter before rebounding to 943, on average, in the fourth quarter, allowing shale production to grow by 500,000 bpd this year.
Three states lost three oil rigs this week, Alaska, Oklahoma and Texas, the state with the highest number of rigs.
The Niobrara shale in Colorado and Wyoming was the basin with the biggest oil rig loss this week, down three to 21 rigs, the lowest since January 2013.
The number of rigs drilling for oil in Canada fell to 18, the lowest since 2009.
U.S. natural gas rigs meanwhile fell by nine to 233, the lowest on record, according to data going back to 1987. (Reporting by Scott DiSavino; Editing by Marguerita Choy)