WASHINGTON — The Supreme Court on Thursday decisively sided with Oklahoma and rejected Texas' claim that it has a right under a 30-year-old agreement to cross their common border for water to serve the fast-growing Fort Worth area.

The justices unanimously said that the Red River Compact "creates no cross-border rights in Texas."

The case concerns a dispute over access to southeastern Oklahoma tributaries of the Red River that separates Oklahoma and Texas.

The Tarrant Regional Water District serving an 11-county area in north-central Texas, including Fort Worth and Arlington, wants to buy 150 billion gallons of water and said the four-state compact gives it the right to do so. Arkansas and Louisiana are the other participating states, and they sided with Oklahoma.

"Obviously, we are disappointed with the Supreme Court's decision. Securing additional water resources is essential to North Texas' continued growth and prosperity and will remain one of our top priorities," water district general manager Jim Oliver said.

Justice Sonia Sotomayor's opinion for the court made plain that the justices did not find this a close case. "We hold that Tarrant's claims lack merit," Sotomayor said.

The case arose from a federal lawsuit the district filed in 2007 against the Oklahoma Water Resources Board and the Oklahoma Water Conservation Storage Commission that challenged the state's water laws and sought a court order to prevent the board from enforcing them.

Lower courts ruled for Oklahoma, including the Denver-based 10th U.S. Circuit Court of Appeals. It found that the Red River Compact protects Oklahoma's water statutes from the legal challenge.

Legislation adopted by the Oklahoma Legislature in 2009 said no out-of-state water permit can prevent Oklahoma from meeting its obligations under compacts with other states. It also requires the Water Resources Board to consider in-state water shortages or needs when considering applications for out-of-state water sales.

The Obama administration backed the Texas district at the Supreme Court, saying Oklahoma may not categorically prohibit Texas water users from obtaining water in Oklahoma. But the administration took no position on whether the Texans ultimately should get the water they are seeking in this case.

The case is Tarrant Regional Water District v. Herrmann, 11-889.