Oil and Gas Minister Bayramgeldy Nedirov said the proposed Turkmenistan to India pipeline, known as TAPI, would require 1 trillion cubic metres of Turkmen gas to be pumped over a 30-year period.
"Preparations are under way for the imminent signing of an agreement on the sale and purchase of natural gas," Nedirov told an international investment forum.
"There are no doubts that this project will be realised."
He did not give further details about the signing or who the counterparts would be.
Turkmenistan, a Central Asian republic sitting on the world's fourth-largest natural gas reserves, wants to build the pipeline as part of its plans to diversify sales from Soviet-era master Russia to energy-hungry markets in Asia and Europe.
The idea of the 1,700-km (1,056-mile) TAPI pipeline was first raised in the mid-1990s, but has never been realised.
Pakistan and India, which would consume most of the gas supplied via the pipeline, have previously said they are close to signing a supply deal with Turkmenistan. Previous timeframes have passed without an agreement being struck.
The security of a route that would run through Taliban heartlands in southern Afghanistan mean security will be a major challenge to the project, which proposes annual supplies of 33 billion cubic metres (bcm) of Turkmen gas.
An intergovernmental agreement signed in the Turkmen capital Ashgabat in December contained no specific provisions for security, volumes or gas prices. The partners must also secure funding for the pipeline.
Turkmenistan envisages that gas for the pipeline would be supplied by its South Iolotan field, ranked by British auditor Gaffney, Cline & Associates last month as the second-largest in the world behind Iran's South Pars deposit.
The auditor said South Iolotan contained between 13.1 trillion and 21.2 trillion cubic metres of natural gas.
A government official, speaking on condition of anonymity, told Reuters on the sidelines of the forum that Turkmenistan also planned to sign another gas supply deal with China.
"Signing could take place during an official visit by President Kurbanguly Berdymukhamedov to Beijing, which could take place in the near future," he said, without giving further details.
Turkmenistan has said supplies to China could rise to 17 bcm in 2011 and 20 bcm in 2012. The countries plan eventually to raise annual supplies to 60 bcm, equivalent to more than 60 percent of China's domestic gas output in 2010.