Oil-bearing fluid inclusions trapped within authigenic K-feldspar in Late Jurassic reservoirs throughout the UK Atlantic margin are evidence for an early oil migration event from Late Jurassic source rocks in the Faeroe-Shetland Basin. Previous compound-specific isotope studies confirm the hydrocarbon provenance. Temperature-composition-time data show that the Late Jurassic source rocks were oil mature 113 ± 3.5 Ma (2σ). This new 40Ar/39Ar authigenic K-feldspar age shows that the Late Jurassic source rocks were oil mature 30–40 m.y. prior to current estimates.