North Dakota’s drilling rig count dipped below 100 on Wednesday, a level not seen for more than five years and one that state officials expect will not be enough to maintain existing oil production of 1.2 million barrels per day.

There were 98 rigs operating in the state on wells owned by Exxon Mobil's XTO Energy, Norway's Statoil and others, according to data from the state's Department of Mineral Resources (DMR).

That is down from 120 at the start of the month and 198 last March.

Lynn Helms, the DMR's head, had said earlier this month that he did not expect the rig count to fall below 100, and warned that even at that level, "we could see production numbers drop off."

While the rig count can sometimes prove to be a harbinger of future oil production, its reliability as such a barometer is slipping due to technological advancements.