You searched for: “ad val
ad valorem (ad vuh LOH ruhm); ad val., ad v., a/v; ad valorem tax (Latin)
Translation: "According to value or per unit of value, meaning that it is divided by the price."

Many states and federal governments tax energy extraction in this manner.

Ad valorem also refers to taxes as "In proportion to invoiced value of goods." A term used when imposing customs and stamp duty, the duty increasing according to the value of the transaction of goods involved.