The formation of calcium carbonate mineral scale is a persistent and expensive problem in oil and gas production. The aim of this paper is to further the understanding of scale formation and inhibition by in-situ probing of crystal growth by synchrotron radiation wide angle X-ray scattering (WAXS) in the absence and presence of polyphosphinocarboxylic acid (PPCA) scale inhibitor. This technique offers an exciting prospect for the study of scaling. It has been shown that the nucleation and growth of various calcareous polymorphs and their individual crystal planes can be followed in real-time and from this the following conclusions are reached: The process of scale depositing on the surface can be divided into an unstable phase and a stable phase. PPCA lengthens the induction time of the surface deposition process. PPCA suppresses calcite formation and results in vaterite-dominated scale. PPCA causes a change of lattice parameter for both calcite and vaterite crystals. The c-axis of unit cell increases and the a-axis and b-axis of unit cell decrease. (C) 2008 Elsevier Ltd. All rights reserved.