Tanker freight is quoted in Worldscale points, written as WS followed by a number. WS100 does not mean one hundred dollars of anything. It means one hundred percent of a published notional rate specific to that route, and that notional rate is recalculated annually.
The reason for this apparently baroque system is real. There are thousands of possible route pairs, and a rate quoted in dollars per tonne would be incomparable across them: a short Mediterranean voyage and a long Gulf-to-Asia voyage have completely different cost structures, so the same dollar rate means very different profitability. Worldscale solves this by publishing, each year, a flat rate per tonne for every standard route, computed on a standard vessel with standard assumptions about speed, port time, and bunker prices. Quoting a percentage of that flat rate makes rates comparable: WS80 on two different routes means roughly the same relative market strength on both.
The flat rate revision is itself informative in one respect: because the calculation assumes a bunker price, a large move in fuel costs during a year makes the current flat rates stale, and the market compensates by trading at WS levels further from 100 than the underlying economics would otherwise suggest. A very high WS number can therefore partly reflect an out-of-date flat rate rather than an extraordinarily strong market.