Over the last two weeks, the maritime world has watched with horror as a tragedy has unfolded in the East China Sea. A massive Iranian tanker, the Sanchi, collided with a Chinese freighter carrying grain. Damaged and adrift, the tanker caught on fire, burned for more than a week, and sank. All 32 crew members are presumed dead.

Meanwhile, Chinese authorities and environmental groups have been trying to understand the environmental threat posed by the million barrels of hydrocarbons that the tanker was carrying. Because the Sanchi was not carrying crude oil, but rather condensate, a liquid by-product of natural gas and some kinds of oil production. There has never been a condensate spill like this.

While it might seem that all oil spills would at least be similar, in this case that is not true. Underground, crude is a liquid you can pump. Condensate, on the other hand, is a gas amid the heat and pressure down there. Bring it up to the surface and it condenses into liquid. This liquid is made of hydrocarbons like crude—and is sometimes classed as a form of it—but contains a different mix of molecules than other crude oils.

That mix is substantially lighter, containing more small, simple molecules and fewer large, complex molecules. This composition—and the composition of any form of petroleum—is highly significant for the refiners who turn raw petroleum products into refined fuels and chemicals that they sell. But, in this case, the properties are salient to the disaster and the environmental aftermath.

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