Troll is a field in the northern part of the North Sea. The water depth is 300-330 metres. Troll was discovered in 1979, and the initial plan for development and operation (PDO) was approved in 1986. The plan was updated in 1990 and involved the transfer of gas processing to the Kollsnes terminal. Production started in 1995. A phased development was pursued for the Troll field, with Phase I recovering gas reserves in Troll Øst and Phase II focusing on the oil reserves in Troll Vest. Troll Phase I has been developed with Troll A, which is a fixed wellhead and compression facility with a concrete substructure. Troll A receives power from shore. The gas compression capacity at Troll A was increased in 2004/2005, and again in 2015. Troll Phase II was developed with Troll B, a floating concrete accommodation and production facility, and Troll C, a semi-submersible accommodation and production steel facility. The oil is produced from several subsea templates tied-back to Troll B and Troll C by pipelines. Production from Troll C started in 1999. The Troll C facility is also utilised for production from the Fram field. Several PDO amendments were approved in connection with various subsea templates at Troll Vest. The latest PDO amendment was approved in December 2018 for the Troll Phase III development: gas blowdown in Troll Vest.