The accord is aimed at building new natural gas export pipelines from the Caspian Sea to European markets, amid competition with Russia for transit routes and clients.
It was signed by U.S. Secretary of State Condoleezza Rice and Azerbaijan's foreign minister, Elmar Mammadyarov.
The accord expresses the intention of the U.S. and Azerbaijani governments to convene a high-level dialogue on energy security in the Caspian region.
Following the signing ceremony, Mammadyarov told RFE/RL that the agreement, if successfully implemented, could be worth billions of dollars in the long term.
U.S. officials said the memorandum of understanding is an important element in Washington's growing partnership with Azerbaijan, which includes cooperation on energy, democratic and market economic reform, and security.