Total and CNPC each now own a one-third stake in the Bokhtar venture, in Tajikistan, while Tethys's 85% owned Kulob Petroleum subsidiary has the other third.
Additionally, the Tajik authorities have awarded the partners new acreage - a further 1,186 square kilometres - in the area. Also, the initial period under the production sharing contract has now been extended until 2020.
Under the terms of the farm-out Kulob will receive a US$63mln payment for past costs, as well as a 'carry' on future work of up to US$80mln. As a result, it expects that it will only have to contribute US$9mln to the 2014 work program.
It says the details of next year's plans will be announced shortly, but the deal will allow the consortium to progress exploration plans with further seismic acquisition and the drilling of deep exploration wells to test the potential giant deposits thought to be present in the area.
The area is an extension of the Amu Darya Basin, which, according to a statement released by Tethys, contains some of the world's largest gas and condensate fields.
"We believe the Bokhtar PSC is a world class asset with enormous potential," Tethys president Dr David Robson said.
"The strengths brought to this project by our new partners, Total and CNPC, means we are in a position to rapidly explore and develop this potential using all available techniques and technologies and with the financial strength to maximise success."
The Bokhtar production sharing contract area is believed to host a massive 27.5 billion barrels of oil equivalent, comprising 114 trillion cubic feet of gas and 8.5 billion barrels of oil.
The joint venture will be operated by the Bokhtar Operating Company, which is owned by the three partners.
Tethys Petroleum has a strong foothold on its assets in Central Asia with enormous potential for future growth. Aside from Tajikistan, the company also holds properties in Kazakhstan and Uzbekistan, where just last month the company signed a Protocol of Intent with the Uzbek State oil and gas company, Uzbekneftegaz (NYSEARCA:UNG), for exploration work in the North Ustyurt Basin of Northern Uzbekistan.
In London, Tethys shares were up 4.5% after the announcement. The stock has more than doubled since early December.
Disclosure: I have no positions in any stocks mentioned, and no plans to initiate any positions within the next 72 hours.