Today three Northeast Asian currencies moved in three directions. The won was weakest: USD/KRW rose 1.0292 to 1,339.94, a depreciation of more than 1% in a single day. The yen weakened in step, with USD/JPY at 158.17, while only the yuan moved against the grain, USD/CNY easing to 6.6661. This kind of divergence is not the norm and it hits the region's refiners and bunkering ports directly.

Korean refiners hold large dollar-denominated crude purchase books. A weaker won lifts the won cost of the same barrel of Brent. Korean refiners already earn on location and run rates across Northeast Asia's surplus product exports; now the feedstock side adds won cost on top, squeezing margins between international oil prices on one side and the local currency on the other.

Busan, as a Northeast Asian transshipment bunkering port, shifts too. A weaker won means foreign owners bunkering in dollars pay relatively less, which in theory helps Busan win ship calls; but by the same logic the Korean domestic refiner's landed cost gets dearer, so the supply side and the refiner side move in opposite directions — you cannot read only one face of it.

By contrast a stronger yuan trims China's dollar crude landed cost, giving the outer Shanghai port and Zhoushan more room on bonded bunkering. Three currencies diverging effectively reshuffle the region's bunkering and refiner-profit map; who gains depends on which book you are reading.