Abstract Knowledge of subsurface stresses is critical to management and prediction of fluid behaviour in the Earth's crust. However, uncertainties associated with the estimation of vertical stress magnitudes are rarely explored. In settings where the principal stresses are close, small changes of only a few MPa can have drastic effects on, stress regime prediction, fault reactivation and expected fracture behaviour. Using petroleum datasets from the Moomba Gas Field in the Cooper Basin, Australia, we assess the effects of interpolation between gaps in density wireline logs that have been filtered to remove sections of poor density tool contact in coal-bearing sequences. In addition, we compare the sonic velocity–density Nafe–Drake and Gardner transforms by comparing estimates of density from sonic velocity against density from wireline logs. The results indicate that vertical stress could be underestimated by c. 3 MPa at c. 3 km in well Moomba 61, using traditional methods. The Gardner transform shows a stronger correlation between sonic and density values for rocks in the Cooper Basin. However, once calibrated to the regional sonic velocity–density trend, the Nafe–Drake transform better matches the density logging tool in Moomba 61. This study delivers a more robust workflow for estimating the vertical stress in basins with deep coal-bearing strata.