Petroleum production wastewater is highly saline and contains large amounts of Ca, Mg, sulphides and hydrocarbons. The reuse of this wastewater in the secondary oil recovery can provide pollution prevention and water conservation benefits. Injection of water to the oil deposits is a frequently used method for secondary oil recovery. This operation is performed at high pressures and temperatures, because of which a suitable water quality is required to avoid deposit formation, scaling and clogging effects. The objective of this study was to select the best treatment system for the oil production wastewater, generated in one of the Mexican oil extraction facilities, for the implementation of this kind of reuse by injecting the treated water to sand formations with 12–15% porosity. A complete characterization of the petroleum production wastewater was done. Based on laboratory tests, three basic treatment options were suggested and evaluated in a pilot plant. The most suitable treatment was determined by injecting the different treated waters in samples of the real formations. The selected system consists in softening, followed by oxidation, decarbonation and filtration. This train allowed 99.8% hardness removal, a complete S2− removal, as well as 99% TSS, 78% TOC, 98% Sr, 86% Ba, 51% Si and 17% Fe removals.