Your link says ND royalties are 18.75%. Ms. Coyne's numbers (20%) don't seem far off. She got them from the ND Tax Dept. and said they were the average for the state.
Look at Alaska’s numbers from the department of Revenue.
$8,090,100,000 revenue from oil
191,260,000 barrels of oil
Alaska North Slope Average Price $87.32
Dollar Value in Alaska of all oil produced = $16,700,823,200
Percentage paid to the State = 48.4%