Saudi Arabia is planning to buy large volumes of American natural gas for the first time, signaling a new strategy for its state-owned company Saudi Aramco and the growing importance of the United States as an energy exporter.

Saudi Aramco has reached a preliminary agreement with Sempra Energy to buy five million metric tons of liquefied natural gas a year for 20 years, the companies said on Wednesday. The gas will be shipped from an export terminal that Sempra plans to build in Port Arthur, Tex. Aramco intends to buy a 25 percent equity stake in that terminal as part of its deal with Sempra.

The Saudi energy giant has previously indicated that it wants to make large investments in the United States, where the shale-drilling boom has produced a glut of cheap natural gas over the last decade. The United States has become one of the major exporters of natural gas in recent years, along with Qatar, Australia and Russia. Gas is increasingly replacing coal as a fuel for power plants around the world.

Qatar Petroleum, a competitor of Saudi Aramco’s, said in February that it was investing in a gas export terminal in Texas with Exxon Mobil.