The black oil equation of state has for the last century been integral for modelling fluid behaviour in the petroleum industry. Despite the rise of compositional approaches, the black oil equation of state remains widely used in reservoir and process simulations. Traditionally, black oil modelling focuses on the volumetric behaviour of fluids, but it also requires thermophysical properties like heat capacity and thermal conductivity. This study introduces novel empirical correlations for pressure and temperature dependent isobaric specific heat capacity and thermal conductivity of undefined petroleum liquid fractions. Although pressure has a minimal impact on heat capacity, it significantly affects thermal conductivity, making it an essential parameter to include. Four correlations were developed: two for each property, with one set based on in situ density and the other on specific gravity. Statistical analysis reveals that the correlations using in situ density offer higher accuracy. These new correlations outperform existing models, providing a reliable calculation method in early project phases and screening tasks within chemical and process engineering.