A photo taken on August 19, 2013 shows a worker checking oil tanks at an oil well near Tioga, North Dakota.

Oil prices dropped on Friday, cutting into a winning month for crude.

West Texas Intermediate futures fell more than 4% to settle at $55.17, posting a 4.1% loss for the week and snapping a 3-week winning streak. Trading volume was lighter than usual Friday, and crude did still manage to finish the month with a 2.3% gain. European Brent futures fell $1.44 to settle at $62.43. For the month prices were up 6%, making it the best month since April.