Since production began in the HP/HT Kristin Field off mid-Norway, reservoir pressure in each of the three mid to late Jurassic reservoir units (the Garn, Ile and Tofte formations) has declined significantly more rapidly than was initially predicted. In the Garn Formation, the Tofte Formation and to some extent also the Ile Formation, this has occurred at least partly because an unusual distribution of reservoir properties led to bias in the four-well appraisal dataset and this in turn resulted in an overestimation of reservoir properties. Of particular importance to this bias was the fact that very good but unrepresentative reservoir properties were encountered in all three reservoir zones in the discovery well located in the centre of the field. These, it is now realized, are not even typical of most of the central part of the field but are, instead, restricted within one, small, anomalous area. Study of cores and thin sections indicates that in each reservoir unit this directly reflects a concentration of more energetic depositional facies in the area while less energetic facies are present on three sides. This pattern was not predictable from the original dataset and seems to have arisen because there was structural control upon facies positioning during accumulation of the reservoir section. This influenced the distribution of cleaner, coarser grained, more proximal depositional facies and, ultimately, reservoir quality distribution and pressure development. What is interesting about Kristin Field is that the structural influence upon sedimentation is observed within the footwall stratigraphy of a major relay structure where the primary provenance direction was on the hanging-wall side. This pattern is the reverse of what is normally reported in tectono-stratigraphic studies.