The ship, a Singapore-flagged tanker, hit a bridge while approaching a dock the South Korean port city of Yeosu Friday.
Kim Sang-bae, director of the regional South Korean Coast Guard, said the collision caused three pipelines to rupture, spilling about 1,000 barrels of oil, China's official Xinhua News Agency reported.
That was about 25 times more than South Korean officials initially estimated, Xinhua said.
Energy news website Platts reported there was no oil spilled from the tanker itself. It said the vessel was chartered by Shell to carry oil from the North Sea.
South Korean Coast Guard officials told Platts it would take a few weeks to clean up the shore and that most of the oil on the water was cleared.
Ocean Tankers, the Singapore company operating the ship, said there were no injuries reported.
The tanker had minor damage and was anchored safely at port, officials said.