The acquisition will provide SSE with around 8% of the gas it needs to supply customers
Perth-based Scottish and Southern Energy has agreed to buy gas assets from the American firm Hess for £278m.
The company said the acquired assets would provide around 8% of the amount it needed daily to supply its customers and power stations.
SSE said there was the possibility of finding more gas through further exploration.
The acquisition is part of a trend for energy providers to gain more control of the wholesale gas market.
Last year Centrica, which owns British Gas and Scottish Gas, won its battle to buy Aberdeen-based oil and gas firm Venture Production.
The deal will include Hess' 18% stake in a BP-operated gas pipeline running from the central North Sea to a processing terminal in Teesside.
Ian Marchant, chief executive of SSE, said: "These assets will provide a new source of primary fuel and a hedge for our gas generation and supply activities.
"The acquisition will also give us involvement throughout the gas chain - production, transmission, storage, distribution and supply."
Hess is a New York-based exploration company with interests throughout the world.