In this study, experimental methods and a theoretical model are developed with aim of understanding and predicting the onset of steam pressure-induced delamination. Experiments are performed by rapid heat-up of moisture saturated T650-35/HFPE-II-52 graphite/polyimide laminates, pre-implanted in the midplane with circular starter cracks. The deformation of these flaws and subsequent delamination growth is measured using custom designed, transverse extensometers. A theoretical model for calculation of internal steam pressure within a deforming circular cavity is derived and combined with a linear elastic fracture mechanics approach to predict the onset of delamination growth. The experimental results and theoretical calculations are used to highlight the effect of heating rate, initial flaw size, initial moisture content, and material toughness on steam-induced delamination. A parametric study is conducted and used to identify conditions required for transition between steam-induced delamination and steam-induced blistering damage.