Leaders of all five states bordering the Caspian Sea are meeting on Tuesday in Turkmenistan to address the decade-long dispute over borders and access to the oil-rich sea. The two-day summit in the Turkmen capital Ashgabat will join the hosts with the leaders of Russia, Iran, Kazakhstan and Azerbaijan. The Caspian is believed to hold the world's third largest oil reserves after the Persian Gulf and Siberia and the dispute has delayed full exploration of the sea's resources. Before the fall of the Soviet Union, access to the Caspian was regulated by treaties between the Soviets and Iran - giving those countries equal share - but with the emergence of new countries on the coast, those treaties are now outdated. At issue is whether the sea should be divided into five equal parts or according the length of the countries' coastlines. The BBC correspondent in Tehran says a significant breakthrough is highly unlikely. Iran's President Mohammad Khatami faces strong domestic pressure not to make concessions on his country's stake in the Caspian, considered by many Iranians as a historic national birthright, not to be bargained away. (BBC)