Via STRATFOR (subscription required), an interesting look at a potential land route for Turkmen gas to Europe:

With Russian opposition to the Trans-Caspian pipeline likely to impede its construction for the short to medium term, Turkmenistan is looking for a land route to reach European consumers. The pipeline network has about 10 billion cubic meters of spare capacity, but it is completely disconnected from Iran’s central gas transportation trunklines (known as the Iran Gas Trunkline), which severely limits Turkmenistan’s ability to pump natural gas through Iran and into Turkey. Iran’s mountainous terrain and the vast desert regions of the Iranian plateau have prevented Iran from linking its own energy supplies to northeastern Iran, much less bringing Turkmen natural gas supplies to the West.
Iran needs to expand its domestic infrastructure significantly before it could transport either internal or Turkmen natural gas. Iran intends to expand its Iran Gas Trunkline network, but currently there are no plans to extend the network toward the northeast. Turkmen natural gas does service the northern coastal region near Rasht, but Iran’s Alborz mountain chain makes westward expansion of this line into Iran or toward Azerbaijan costly and difficult. Iran would likely need foreign investment and assistance to build out its transit network. Even if sanctions are lifted, Iran will likely prioritize the development of its own reserves and export capabilities before lending assistance to Turkmenistan.

The Turks and the Europeans also will need to expand their own transit options to accommodate greater Iranian and Turkmen supplies. Turkey is in the early stages of building the Trans-Anatolian pipeline project to bring natural gas supplies from Azerbaijan’s Shah Deniz II field to southern Europe. Though some spare capacity (less than 10 billion cubic meters) has been built into the design, final routing for the pipeline, future expansion plans and European infrastructure development are still firmly stuck in the planning and negotiations phase, meaning Turkey’s infrastructure limitations compound those of Iran and Turkmenistan.