Concrete spalling results primarily from a thermo-mechanical process because of high thermal gradients, and a moisture-clog process because of the build-up of pore-water pressure. This paper attempted to isolate these mechanisms and quantify their magnitude. Twelve reinforced concrete panels were tested under hydrocarbon fire conditions. The test conditions included different thicknesses, concrete strengths, and specimen sizes. The panels were tested with no additional loading except self weight, and instrumented with in situ thermocouples and pore-pressure gauges. Spalling was quantified according to mass loss and visually represented by three-dimensional (3D) contour surface plots. The research presented for the first time a method to quantify spalling as mass loss in terms of water mass and solid mass. The continuous moisture transport during heating produces a saturated drying front, causing strength degradation and cracking that allows water pooling on the nonexposed fire side. The moisture transport plays an important role in all the mechanisms that contribute to concrete spalling.