Refineries and terminals undertake mass and volume balances every month. After accounting for all known losses, adjustments for bias errors and other known procedural errors, they report a net loss under the name of "unknown" or "unaccounted" for loss since the net loss can no longer be explained. This unknown loss is no longer a mystery.

The concepts presented provide a tool and a methodology to account for most of the currently reported unknown loss in most locations. This, thus, enables local managements to bring a closure (or almost a closure) to their monthly mass (volume) balances.