Paste a car number or type a company name. See who the mark belongs to, what the suffix says about the equipment, and the canonical form of the car number — the one that matches whether it came off a stencil or off a railroad feed.
Type a reporting mark to see who it belongs to.
Every piece of rail equipment in North America carries two things: a reporting mark of one to four letters, and a number of up to six digits. The pair is unique across the continent, which is what lets a car be tracked across dozens of railroads that otherwise share no systems at all.
The last letter of the mark is the part people miss. A mark ending in X is private equipment — a shipper’s car or a lessor’s. Z is a trailer or chassis, U is a container, and a mark with none of those belongs to a common carrier railroad. So UTLX is Union Tank Car’s fleet, while UP is Union Pacific itself.
Three limits worth holding onto, because each one has caused a real billing argument.
The mark is not the hauler. It names the owner or lessee of record. A leased car spends its life on other railroads’ track carrying someone else’s product, and the mark changes none of that.
The mark is not the shipper. An X suffix often points at a leasing company rather than the company whose freight is inside, so reading ownership off the car is a reasonable first guess and a poor final answer.
Marks outlive the companies that earned them. Acquired railroads keep their stencils for years, and one owner routinely holds half a dozen marks. A mark is a pointer into a registry that changes, not a permanent fact about a company.
A bill of lading prints the AAR stencil form, zero-padded to six digits. An operator typing the same car into a system, or a railroad feed reporting it, uses the human form without the padding. STFX000010 and STFX 10 are one physical car, and any system that treats them as two will duplicate the car, split its inventory, and bill the customer twice for one move.
The fix is canonical matching on padding only — never fuzzy matching. WFRX86709 and WFRX806709 differ by an interior digit, and treating those as the same car attaches one customer’s inventory to another customer’s physical equipment. Rebulk’s car tracking normalizes exactly this way, which is why a BOL arriving after a railroad sighting merges into the same car instead of opening a second one.
4,084 marks, compiled 2026-09-19 from Wikipedia’s list of reporting marks, used under CC BY-SA 4.0. Modified from the original: the source pages were parsed and normalized — wiki markup stripped, owner lists split into separate names, and the per-letter pages merged into one dataset. No entries were edited for meaning. It is a reference, not a register of record: new marks are issued regularly, and this list will lag them. The authoritative sources are Railinc’s Mark Register for the letters themselves and Umler for what a specific car actually is — both from Railinc, the AAR subsidiary that maintains them.
The two-to-four letter code stencilled on every piece of North American rail equipment, paired with a one-to-six digit number. Together they identify the car uniquely across the continent — two cars can share a number as long as their marks differ. The letters are assigned by the AAR under authority from the Surface Transportation Board, Transport Canada, and the Mexican government, and maintained by Railinc.
Read the mark off the car — it is on the left side, usually the bottom left corner, and on each end — and look the letters up. This tool covers the published mark lists. For the authoritative owner of a specific car, including lessee and current registration, the system of record is Railinc's Umler, which is a paid subscription.
The car is privately owned rather than railroad owned. X marks belong to shippers like Cargill (CRGX) and DuPont (DUPX), and to leasing companies like GATX, Trinity (TILX), and Union Tank Car (UTLX). A Z suffix means a highway trailer or chassis; a U suffix means a container, coordinated internationally rather than by the AAR alone.
No, and this is the most common misreading. The mark names the owner or lessee of record. A GATX tank car can spend its entire life on other railroads' track, hauling a shipper's product under a lease. The mark tells you whose asset it is, not who has custody of it today or whose freight is inside.
Because marks outlive mergers. When one railroad absorbs another it often keeps the legacy marks in service rather than restencilling a fleet — CNW marks remained after Union Pacific absorbed the Chicago & North Western, and KCS marks are still around after the 2023 CPKC merger. One company also commonly holds several marks: the GATX companies have used GATX, GACX, GABX, GAEX, GASX and more.
Usually leading zeros. A bill of lading carries the AAR stencil form with the number zero-padded, like STFX000010, while an operator or a railroad feed types the human form, STFX 10. They are the same physical car. Padding is not identity — but an interior digit is, so WFRX86709 and WFRX806709 are two different cars, not a typo of each other.
Rebulk ties each railcar to its BOL, its material, its customer, its demurrage clock, and its scale tickets — matching the car number the way the industry actually writes it, stencil or shorthand.
