Starting Jan. 1, the vast majority of the world’s ships were forced to change the fuel they use. Some big winners — and potential losers — are starting to emerge from what was a historic switch for the world’s oil refining and maritime industries.

Shippers have fewer than three weeks until new rules kick in forcing them to burn cleaner fuels, but the regulations are already redefining key trade routes in the global oil-product markets.

They may still be six months away, but new rules on marine fuels are already sending shock waves through the little-known world of refinery feedstocks.

The International Maritime Organization rejected a proposal — supported by both the U.S. and shipping groups — for a phased start to rules that will limit the sulfur content of ship fuels starting in 2020.

A.P. Moller-Maersk, the world’s largest container shipping line, said adhering to stricter environmental standards could add at least $2 billion to its annual fuel bill from 2020.