The real issue that fuel oil is so cheap. If customers are paying for the fuel, and fuel was a significant cost, then they'd certainly be interested in shopping

The real issue that fuel oil is so cheap. If customers are paying for the fuel, and fuel was a significant cost, then they'd certainly be interested in shopping around for a ship that can offer lower fuel consumption. But fuel oil is really just a byproduct of refining crude. It's the muck left over when you've extracted everything else that's useful. And of course, it is not taxed, so prices don't account for it's environmental externalities. If we can reduce overall demand for petroleum products, this should eventually cause fuel oil prices to rise because there'll be less crude being refined, and thus reduced supply.