Calcination involves heating green coke to temperatures above 1200°C to drive off residual hydrocarbons and moisture, producing a denser, more electrically conductive material. Customs classification hinges on whether this thermal treatment has occurred: not-calcined (green) coke retains volatile matter typically above 8–10%, while calcined coke falls well below that threshold. A manufacturer's process declaration or laboratory volatile-matter analysis supports the correct heading determination.

Petroleum coke itself does not require an EPA import permit, but its end-use as a fuel is subject to Clean Air Act regulations governing sulfur emissions at the burning facility. Importers supplying petcoke to domestic fuel users should be aware that high-sulfur grades may face restrictions on combustion in certain air-quality attainment areas, which can affect demand and pricing even if the import itself clears customs without additional agency review.