Hydrothermal liquefaction (HTL) of macroalgae offers a promising route to advanced biofuel production, although the distinct biochemical compositions of different macroalgae species can lead to widely different product yields and compositions. On the basis of this, there is an implicit assumption that there exists a universal optimal feedstock species for a bioenergy-based biorefinery, which could be exploited across a wide region. However, no studies to date have examined the effect of this large geographical variation on a single macroalgae species for biofuel production. In this study, 24 samples of Ulva intestinalis were collected along 1200 km of Swedish coastline and assessed as a feedstock for HTL. Significant variation in composition was observed between samples from Baltic and Atlantic regions, but substantial variation also existed between sites within close proximity. This was reflected in the HTL biocrude oil yields, which varied between 9 and 20% (14-28% dry and ash-free basis) across the sample set. In a number of cases, greater variation was seen for adjacent sites than for sites at opposite ends of the sampling spectrum. Biocrude oil yields in this study also differed substantially from those previously obtained for U. intestinalis from the United Kingdom and Vietnam. Localized environmental conditions affected the HTL product composition significantly, in particular, the elemental distribution within the sample set. The variability observed in this study suggests that no single species will be dominant within a macroalgal biorefinery concept, but rather a species would need to be selected to match the needs of the exact local environment.