Abstract
Thesis assess operators ability to deliver accumulated gas forecasts for 40 fields on the Norwegian continental shelf (NCS) that received Plan for Plan for Development and Operations (PDO) approval in the years 2000 to 2020. The analysis is conducted both with and without including schedule delays. The results indicate that operators forecasts are heavily influenced by optimism and overconfidence bias resulting in significantly lower production than forecasted and that was the basis for the investment decisions. However, this study shows that the forecasts are particularly poor in the early part of field life and improves toward the end of field lives.