The gas sales agreement between Norway and Poland will be signed in Oslo on the afternoon of 5 May.
Polish prime minister Jerzy Buzek and his Norwegian opposite number, Kjell Magne Bondevik, are due to be present at the ceremony.
It became clear last week that the state-owned Polish Oil and Gas Company (POGC) will buy 500 million cubic metres of Norwegian gas annually for five years from 2001.
The contract will be signed by representatives of Norway's Gas Negotiating Committee and the POGC.