The justices, in a 6-2 decision, said Delaware can block the project, even though it was proposed for Jersey's side of the river.
Delaware said it wanted to stop the project because of safety concerns. The state owns the river bottom most of the way across the waterway, including the land on which a 2,200-foot-long pier would be built on the Jersey side.
The states agree that Delaware owns the land, but Jersey argued that a century-old agreement allows each state to control piers on its side of the river.
Justice Ruth Bader Ginsburg, writing for the court, said Delaware cannot block ordinary projects from going forward. The proposal at issue, however, "goes well beyond the ordinary or usual," Ginsburg said.
Justices Samuel Alito and Antonin Scalia dissented.
The dispute centered on a project that energy giant BP wanted to build on the Jersey side of the river. New Jersey officials approved the project, which could bring more than 1,300 construction jobs.
Delaware officials, however, have refused to authorize the construction of a 2,000-foot-long pier, which would be built on the part of the river bottom that belongs to Delaware. Without the pier, the project could not go forward.
Delaware's lawyer told the court that the state has only twice in 160 years denied permission to build a pier on the Jersey side of the river and both instances involved LNG facilities.
Up to 150 ships a year would dock at the proposed pier, which would be directly across the river from Claymont, Del. Delaware says the proposal raises safety fears because an estimated 22,000 residents living near the river's main shipping channel would be at risk in case of a major accident. BP said the facility would be able to deliver up to 1.2 billion cubic feet of natural gas a day to the Mid-Atlantic region.
A court-appointed special master concluded last year that Delaware has the authority to block the pier.
Justice Stephen Breyer did not take part in the case. He owns $15,000 to $50,000 in BP stock, according to his most recent financial disclosure.
The case is New Jersey v. Delaware, Original 134.