N.D. Cent. Code § 23.1-13-13

In case of a dispute, heating oil must be sold on the basis of the United States gallon containing two hundred thirty-one cubic inches [3785.41 milliliters] at sixty degrees Fahrenheit [15.56 degrees Celsius]. The volume of the delivered oil; however, may be calculated from its weight and gravity degrees API in accordance with the national standard petroleum oil tables prepared by the national bureau of standards.