Effective October, Statoil will increase supplies to 2.5 billion standard cubic metres per year (bcm/y) from the previously agreed 0.5bcm/y.
Statoil marketing and trading senior vice-president Tor Martin Anfinnsen said: "Being the second largest supplier of gas and electricity in the UK, SSE is a significant player in a market that is very important to Statoil.
"The agreement with SSE is another confirmation of Statoil’s position as a long term reliable supplier of gas to the UK."
Statoil already has a deal with SSE signed in October 2011, to supply 0.5bcm/y of gas to St. Fergus terminal, between October 2012 and October 2022.
As part a separate deal with UK utility Centrica, Statoil will supply up to 7.3bcm/y of gas for a 10 year period starting this year.
The agreements with SSE and Centrica represent almost 15% of gas demand in the UK, which can serve around 8.5 million households annually.
SSE Energy portfolio management managing director Jim Smith said: "The significant expansion of our agreement with Statoil is consistent with this strategy, securing a significant volume of gas from a reliable producer with physical links to the UK."
