In situ CO2 enhanced oil recovery (ICE) shows great potential for increasing oil field tertiary recovery. Instead of injecting liquid CO2 directly into the oil reservoir, a solution of a CO2-generating agent is injected to deliver CO2 to the targeted zone. Urea is an attractive gas-generating agent for ICE because it has both low price and exceptional stability in brine with elevated divalent cation concentrations. Besides CO2 urea thermal hydrolysis releases NH3(aq). Both molecules have positive impacts on the tertiary recovery, such as oil swelling, oil viscosity reduction, brine alkalinity increase, and sand surface wettability reversal. Thermal hydrolysis of urea is rapid at 120 degrees C, but the reaction rate decreases exponentially at lower temperatures. This work compares tertiary recovery from urea hydrolysis at 120 and 80 degrees C with and without a homogeneous catalyst (NaOH) for the purpose of examining the feasibility of urea-ICE for low-temperature reservoirs. The tertiary recovery was studied and optimized with data from 11 one-dimensional sand pack tests at varying conditions. Since urea hydrolysis produces a reaction intermediate, ammonium carbamate, which is known to precipitate in the presence of divalent cations, brines with elevated calcium concentrations were studied to examine the divalent cation stability of the proposed system. The optimization work included tests with urea concentrations varying from 1 to 35 wt % and different injection strategies and flow rates (0.03-0.3 mL/min). Tertiary oil recovery results of this study show that there are two different optimal concentrations of urea, one that maximizes the volume of tertiary oil produced and another that minimizes the cost per barrel of tertiary oil produced. The urea consumption of the proposed ICE can be as low as 34 kg/barrel with 2.5 wt % chemical slug, and the tertiary recovery can be as high as 48.3% with 10 wt % chemical injection. The optimal injection strategy was strongly dependent on chemical residence time because the tertiary recovery mechanisms vary with the injected concentrations. The aqueous effluent showed increasing solution pH, approaching pH 10. Based on an high-performance liquid chromatography analysis of the aqueous effluent, the mass balance of different tests was calculated. No adverse effect on tertiary recovery was observed in simulated seawater brines, with up to 1 wt % dissolved divalent salts. At higher levels of divalent ions (Ca2+ 7000 ppm) in a so-called API brine, lower tertiary recovery was observed but there was no evidence of formation damage and tubing blockage. In this work, the proposed ICE system showed superior tertiary recovery performance (48.3%) compared to the most recent efforts by our group (29.5%) as well as similar ICE systems (2.4-18.8%) proposed by others. Results illustrate the economic feasibility and the divalent cation tolerance of the urea-ICE process.