C-80 tetra-acid (also known as ARN) is a molecule present in crude oil that can precipitate during oil production in basic medium and in presence of calcium ions to form deposits. The formation of such deposits is detrimental in production because they can plug oil production facilities and may lead to costly production shutdowns due to deferment and dean up operations. To better understand this reaction, the solubility of a model molecule mimicking the properties of C-80 tetra-acid (named BP-10) have been measured in an oil/water system, using chloroform as oil in presence of calcium to establish quantitative relationships between solubility and pH, calcium concentration, temperature, and other parameters. It has been determined that the maximum BP-10 concentration in oil phase (solubility limit) follows the following relationship: [BP-10](o) = A x 10(-4pH), with the fitting parameter A x [Ca2+](2) = 2.6 x 10(18) mol(-1).L+1. This relationship is valid at [Ca2+] >= 10 mM, with a slight overestimation of the solubility at lower calcium concentration from temperatures varying from 5 to 50 degrees C. This relationship holds at any ionic strength (up to 600 mM of NaCl) and total BP-10 concentration (up to 200 mu M) in the system. In presence of Mg2+, the relation is still valid with a different prefactor. For all the studied systems, the concentration of BP-10 in water was very low, lower than 2 mu M. The solubilities of C-80 tetra-acid in oil phase with BP-10 one have been compared. Both molecules have a similar pH range for precipitation, but C-80 tetra-acid has a different relationship between its concentration in oil phase and pH.