Methodology

How the data is collected

Everything on this site comes off the US Energy Information Administration's public API, pulled on a fixed schedule. The weekly on-highway diesel price survey (released Mondays, covering the US average, the five PADDs, three East Coast subregions, California and PADD 5 without California, the complete published set) and the daily ULSD spot series for New York Harbor and the Gulf Coast. There is no scraping, no estimation and no text-extraction step; every figure comes straight off a structured agency series.

Each pull covers a trailing window, not just the newest week, and a missed or partial run backfills on the next one. If one week's job fails, that week fills in automatically once the pipeline runs again; nothing is silently skipped or left blank. Federal holidays can slip EIA's Monday release by a day; the data carries its own dates, so a slipped release shows up as a Tuesday-dated week, not a gap.

Data date versus build date

Every price is pinned to its own data date in the text: "for the week of" the survey Monday, or the spot quote's business day. The "Last updated" stamp on a page is a different thing, the time the site last refreshed that page's data. We keep the two visibly separate so a delayed pull reads as exactly that, rather than dressing old data in a fresh date.

How comparisons are computed

Week-over-week, month-over-month and year-over-year are each the change between the latest value and the value from that many days back on the same series. There is no smoothing or averaging in these figures; they are two readings compared directly.

"Vs 5-year median" compares the current value to the median of that same calendar week across the prior five years. Median, not average, so one freak year (a price spike, a crash) does not skew the baseline. Treat it as a fast, consistent yardstick: if the prior five years were themselves expensive, "at normal" can still mean expensive in absolute terms.

Which direction reads as hot, and why

Every reader of this site buys diesel or prices freight against it, so the colored tags run the buyer's way: a price above its five-year median reads hot (the alarming direction), at or below reads ok. That covers the DOE number, the region pages, the spot pages and the margin proxy. Two sections deliberately carry no tag. Regional spreads cross zero, so a percent-versus-median reading on them is numerically unstable and would color the tag off arithmetic noise; those pages quote the gap in plain cents instead. And cost per mile is the US price restated in a different unit, so its vs-normal signal already lives on the DOE number page; tagging it twice would double-count one signal.

The derived figures, exactly

Four figures on this site are derived, all pure arithmetic on published series. Regional spreads subtract the US average from a region's price for the same survey week; the West-vs-Gulf page subtracts PADD 3 from PADD 5 the same way. Weeks where either side is missing are dropped, never interpolated. The retail-minus-spot margin proxy subtracts the ULSD spot price from a retail price, using the most recent spot quote on or up to five days before the survey date (the survey is Monday-dated and the spot market closes weekends, so this is the nearest business day). Retail includes federal and state fuel taxes and everything else in the retail layer; spot includes none of it. The proxy therefore tracks the whole gap between hub and pump, not a station's margin, and we label it that way. Cost per mile divides the US price by a stated reference efficiency of 6.5 miles per gallon, a plain mid-fleet figure for a loaded Class 8 truck. The 500-mile haul figure is the same reference over a round distance: 500 divided by 6.5 is about 77 gallons, times the price. The reference is stated on every page and every line that shows a per-mile or per-haul number; it is a fixed comparison standard, not an estimate of any particular truck.

Units, stated plainly

Prices are dollars per gallon at EIA's three decimals, with weekly moves quoted in cents. Spreads are cents per gallon. Cost per mile is cents per mile at the stated reference. The retail series is on-highway (taxed pump) diesel; the spot series are ultra-low sulfur diesel, which has been the on-highway spec since 2006.

What we do not compute

We do not forecast anything. We do not model rack prices, station margins, state taxes or your fuel economy. Where a public number does not exist (daily rack prices, per-state weekly surveys beyond California), the site says so rather than substituting an estimate.

How the badges read

Every scored page carries one of three symmetric badges against the 5-year median: "Above normal" (more than 10% above), "Near normal" (within 10% either side), and "Below normal" (more than 10% below). The colors follow the buyer's risk direction: above-normal prices are the alarming side. The badge's hover text carries the date of the data it rests on.

For the plain-English version of how to read a page once the numbers are in front of you, see how to read this.