Found a report about production in North Dakota...the Duperow formation is part of the overall Williston Basin, which covers a huge area.
not sure how to paste the table properly, but if you scroll down the Duperow is the number 2 producer of oil from this Basin historically with over 122million barrels produced
FORMATION BARRELS OF OIL RANKING
Spearfish 421,016 5*
Spearfish/Madison 47,264,282 5
Tyler 73,473,133 4
Madison 765,936,439 1
Lodgepole 12,704,599 7
Bakken (Sanish) 40,309,285 6
Birdbear (Nisku) 5,265,538 10
Duperow 122,890,435 2
Souris River 16,512 14
Dawson Bay 3,525,218 11
Winnipegosis 6,186,977 9
Silurian (Interlake) 55,106,040 5
Stonewall 9,244,665 8
Gunton 164,146 13
Red River 106,282,242 3
Red River "B" 11,378,199 3*
Winnipeg/Deadwood 347,606 12
Total 1,260,516,332
Note: Red River and Red River "B" should be added together for the Red River production total.