Raw volume moves mislead. The z-score divides each move by what is normal for that asset, so the unusual ones stand out.
Field guide entry · written September 23, 2026.
A 20 kb/d swing at a 300 kb/d oil sands project is a quiet month. The same 20 kb/d swing at a 40 kb/d SAGD project is an emergency. Raw moves in thousand barrels per day (kb/d) ignore what is normal for the asset, so sorting by raw change puts the biggest assets at the top every month, whether anything interesting happened or not. Without a normalizer, the biggest-movers table would just be a list of the biggest projects, every single time. Size is not news.
The z-score divides this month's move by the asset's own typical monthly swing over the prior year. Every asset gets judged against itself, on the same scale, from a 300 kb/d mine to a 30 kb/d thermal project. A score near zero means business as usual for that asset. A score of 2 or more means the move was at least twice what that asset normally does in a month. That is the definition of unusual on this site: not big in absolute terms, but big relative to the asset's own history. Standardized moves separate signal from noise; raw moves cannot.
The table still sorts by raw change, because size matters too. The signal flag marks the rows that moved at least twice their normal monthly range. Read the two together. A big raw move with a signal flag is the combination that deserves a trader's attention. A big raw move with no flag is just a big asset being a big asset. Two caveats. The score needs history: fewer than six months of month-over-month changes and the cell reads n/a. And an asset whose history has zero variance gets no score either, because you cannot divide by zero. Both render as n/a, never as zero. The history is the asset's own published actuals from the Alberta Energy Regulator (AER) monthly statistics, the same numbers as the Western Canadian Sedimentary Basin (WCSB) model behind this site. Deterministic, no modeling, no projections.
Traders drown in big numbers. The z-score is how you decide which ones earn your attention: standardize the move against the asset's own history, and the real surprises stand out from the routine noise.