American refineries ran at the top of their range last week, and one reason the number looks so high is that the range keeps getting smaller

Refineries have very little room left.

The Energy Information Administration reported on Wednesday that American refineries operated at 97.4 percent of their operable capacity in the week to 21 August. Measured against the agency's own weekly series, which runs to 1,869 observations since November 1990, that is the highest reading since the week ended 7 September 2018. Only four weeks since the start of 2016 have matched or beaten it, and all four were in 2018.

Two numbers make it, and only one of them is about running harder.

The numerator and the denominator

Gross inputs to refineries were 17,551,000 barrels a day, against 17,175,000 a year earlier, an increase of 2.2 percent. Operable capacity was 18,027,000 barrels a day, against 18,160,000 a year earlier and 18,326,000 two years earlier. The plant base is 133,000 barrels a day smaller than last August and 299,000 smaller than the August before.

Divide this week's gross inputs by last year's capacity and the rate is 96.6 percent rather than 97.4. So of the 2.8 point rise in utilisation over the year, roughly 0.8 of a point is arithmetic on a shrinking denominator. The report states the capacity figures and does not explain them, and no closure or conversion is named in it.

The regional table is where the shrinkage sits. West Coast operable capacity is 2,275,000 barrels a day, down 11.1 percent from 2,558,000 a year ago, and crude inputs there fell 5.2 percent. Gulf Coast capacity rose 0.9 percent over the same period, to 9,888,000.

What came out of it

Not enough to rebuild stocks of the two products that matter most.

Total motor gasoline inventories fell 2.5 million barrels in the week, to 206.8 million, which is 7.0 percent below a year ago and about 6 percent below the five-year average for the time of year. Distillate fuel oil fell 2.2 million barrels, to 103.4 million, 9.5 percent below a year ago and about 14 percent below the five-year average. Commercial crude inventories, excluding the Strategic Petroleum Reserve, were roughly flat at 428.9 million barrels and sit 1 percent above the five-year average, so the tightness is in the products rather than in the feedstock.

Demand is not what is emptying the tanks. Total products supplied over the four weeks to 21 August averaged 20.5 million barrels a day, down 3.0 percent on the same period last year. Gasoline supplied was down 1.1 percent, distillate 2.2 percent, jet fuel 2.3 percent.

The reserve kept falling as well. It stood at 289.7 million barrels, down 3.7 million on the week and down 114.5 million on the year, a decline of 28.3 percent.

West Texas Intermediate was $87.21 a barrel on 21 August, $3.22 above a week earlier and $23.13 above a year earlier. The report prints that and offers no account of it, and neither does this item.

Every figure here is a weekly estimate and every one of them is subject to revision.