Topic summary
Fungible

Extracted from the Wikipedia article Fungibility.
Physical goods
Fungible goods include gold, other precious metals, crude oil and many agricultural products. The fungibility of these goods facilitates their trading as commodities. In many cases, fungibility within a type of good is divided by grade and quality. For example, crude oil is divided into Brent Crude, West Texas Intermediate and other grades, which are not all fungible with each other.