The Treaty of Establishment, Commerce and Navigation (or the Treaty of Establishment, Commerce and Navigation with Full Protocols and Annex) was signed on August 25, 1935 between representatives of Iran

Iran

Iran , officially the Islamic Republic of Iran , is a country in Southern and Western Asia. The name "Iran" has been in use natively since the Sassanian era and came into use internationally in 1935, before which the country was known to the Western world as Persia...

 and the Soviet Union

Soviet Union

The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

. This accord helped to reinforce the tenets of the Russo-Persian Treaty of Friendship

Russo-Persian Treaty of Friendship (1921)

The Russo-Persian Treaty of Friendship was signed on February 26, 1921 between representatives of Iran and the Soviet Russia. Based on the terms of the treaty, all previous agreements made between the signatories including the Treaty of Turkmenchay were canceled...

. Based on the terms of the treaty, both signatories reinforced their respective rights to fly their national flags on their respective commercial vessels. Moreover, both signatories were allowed to fish in the Caspian Sea

Caspian Sea

The Caspian Sea is the largest enclosed body of water on Earth by area, variously classed as the world's largest lake or a full-fledged sea. The sea has a surface area of and a volume of...

within ten nautical miles (19 km) of the coastline.

Source

• Mehdiyoun, Kamyar. "Ownership of Oil and Gas Resources in the Caspian Sea." The American Journal of International Law. Vol. 94, No. 1 (January 2000), pp. 179-189.