In Oregon, the larger truck stops, like SpaceAge, Pilot, Flying J,... will post three diesel prices. The lowest price is for PUC plated trucks. The PUC price is about 30c cheaper than the non-PUC cash price to the public. The non-PUC credit price is about 5c higher than the cash price.
If you use the GasBuddy App or similar software on your cell phone, then many times the quoted price is the PUC price, not the non-PUC price. So, if you consult a cell phone App and see a diesel price that is relative too cheap, then you are likely seeing a PUC price. Also, some filling stations sell B20 and that locally is about 20c cheaper than the other stations' non-PUC cash price. But, B20 has less energy than a B0, so you are getting what you pay for.