The major oil reserves in the Dakotas are tied to the Bakken Formation, the same as touted in Saskatchewan.
These oil shales need crude oil prices around $150/barrel before they become profitable to produce. That price is almost here.
Regardless of the amounts, one must be prepared for continuing high petroleum and gas prices.

The U. S. Geological Survey estimate of 400 billion barrels includes portions of the Formation that will be difficult to reach.
Estimates of this sort are always 'guesstimates.' In the Williston Basin area, an article in The Oil & Gas Journal estimates 3-4 billion bbls. recoverable; associated with the oil shales are some reservoirs with liquid hydrocarbons and gas, but nothing spectacular.

Several regions have large deposits of this type, including Australia, Venezuela, China, Colorado, Morocco, etc.

If large areas are brought into production, investor pressure on prices would weaken, but some 10 years' lead-in is needed before large volumes enter the picture.

People blame speculators for price increases in the futures market. Anyone who has savings with any interest-paying institution (banks, credit and retirement funds, etc.), or invests in mutual funds, as well as in industrial stocks and bonds- not just oil company issues or futures- will have part of that money invested in oil. In other words, we are the ones driving the prices, which are still based on supply and demand.