This is common practice with most carriers like a FEDEX, UPS, post offices, etc. There's the contracted rate (or published rate for lower volume shippers) and then a "fuel surcharge" that's tacked on to offset the volatility of fuel and consumables. Usually it's lifted as market conditions change, though not always immediately as each company will often book fuel at a contracted price, even if higher to insure some price stability, so the surcharges don't match market conditions exactly.

With logistics companies it's typically easier to identify the incremental surcharge, as at first glance they've blended it as fee increases.