Two sections of an important pipeline due to bring Caspian oil to Western markets have been connected at a ceremony on the Azeri-Georgian border.
The pipeline is expected to pump up to 1m oil barrels a day
Azeri President Ilham Aliyev said the project, due to be completed next year, would bring great financial wealth and boost regional security.
The multi-billion dollar pipeline from Baku in Azerbaijan to the Turkish port of Ceyhan is backed by Washington.
Russia has proposed an alternative route through its own territory.
"The oil pipeline has united two brotherly nations," Mr Aliyev said at the opening ceremony on Saturday.
"The whole region needs this pipeline."
Georgian President Mikhail Saakashvili said that some forces had tried to stop the project but had failed.
"I have no false illusions that this one pipe will be able to solve all our problems, but this is a start," he said.
"This pipeline marks a major step toward the independence of both Georgia and Azerbaijan," he added.
The Baku-Tbilisi-Ceyhan (BTC) pipeline will run through Georgia to the Turkish port of Ceyhan on the Mediterranean coast.
The project, led by British oil giant BP with the support of the US government, covers 1,760 km (1,094 miles).