Most carbonate formations in nature are oil-wet after organic acids have been adsorbed on the grain surface, which lowers the efficiency of water flooding in the carbonate formations. It has been found that seawater or modified seawater can change an oil-wet carbonate surface to water-wet. To optimize the composition of the brines for better recovery, it is necessary to understand the impacts of the key ions (Ca2+, Mg2+, SO42-) on organic acid adsorption. Benzoic acid (BA) was used as a model acid to study the general adsorption of organic acids on carbonate surfaces. 2D gas chromatography-mass spectrometry (2D GC-MS) analysis verified the existence of BA in a crude oil. We report the adsorption isotherms of BA on calcium carbonate from aqueous solutions using an ultraviolet-visible (UV-vis) method. It was found that the amount of formed calcium benzoate and the impact of ions on the UV absorbance of BA must be taken into consideration for the quantification of adsorbed BA. The results show that the absence of Ca2+ or Mg2+ does not significantly impact the adsorption of BA on CaCO3; however, the absence of sulfate ions can significantly increase the adsorption of BA on CaCO3.