Oil futures fell sharply on Friday, to tally a weekly decline of nearly 10%, as a monthly report from the International Energy Agency raised concerns that the glut of crude supplies and tightening storage capacity in the U.S. may cause prices to weaken further.

Crude-oil for delivery in April fell $2.21, or 4.7%, to settle at $44.84 a barrel on the New York Mercantile Exchange. Prices ended the week with a loss of 9.6%. April Brent crude on London’s ICE Futures exchange shed $2.41, or 4.2%, to settle at $54.67 a barrel, with the front-month contract down 8.5% for the week.

After trading on Nymex ended Friday, the U.S. Energy Department said it plans to buy up to 5 million barrels of crude for the Strategic Petroleum Reserve. Prices in electronic trading edged backed above $45. In its report early Friday, the IEA said any appearance of stability in oil is tenuous. “Behind the facade of stability, the re-balancing triggered by the price collapse has yet to run its course, and it might be overly optimistic to expect it to proceed smoothly,” the report said. Ballooning inventories combined with the nation’s shrinking oil storage could drag prices lower, it said.

The comments from IEA come as oil has been trading in a relatively narrow band over the course of the past few weeks, on the heels of steep declines in weekly U.S. rig counts. Baker Hughes on Friday reported that the number of U.S. rigs actively drilling for oil as of March 13 fell 56 rigs from last week to 866. “Oil rig counts fell for a historic 14th week in a row,” said Phil Flynn, senior market analyst at Price Futures Group. “While at this point the rig count drop has not impacted output, at this rate it soon will.” Flynn also pointed out that the IEA report wasn’t all that bearish as it raised its demand estimate. The IEA forecast average global oil demand of 93.5 million barrels a day for 2015.

Meanwhile, U.S. refinery workers have reached a tentative deal to end a six-week strike.