In the present work a new procedure for evaluation of scale inhibitor for calcium carbonate is proposed based on continuous measurement of particle size distribution by laser diffraction technique and simultaneous pH recording. From data obtained during real-time monitoring of the homogeneous nucleation and growth of CaCO3 particles formed in the bulk phase after the addition of carbonate ions to synthetic formation water (AF-W2), it was possible to evaluate the performance of four inhibitors classified in two groups: phosphonates (ethylenediamine tetramethylene phosphonic acid, EDTMP; diethylenetriamine pentamethylene phosphonic acid, DETPMP) and polymeric inhibitors (phosphino poly carboxylic acid, PPCA; polyvinyl sulfonate, PVS). The comparative bulk crystallization inhibition efficiency for the evaluated inhibitors, under the experimental conditions used in this work, increases in the following order: EDTMP < DETPMP < PVS congruent to PPCA. Moreover, this methodology allowed the deduction of the main mechanism of their inhibiting action: nucleation inhibition or crystal growth retardation. (c) 2014 Elsevier Inc. All rights reserved.4205764Petrobras-CENPESANP [0050.0049964.09.9]ANP [0050.0049964.09.9]