The effect of two different concentrations of olive oil emulsions on development of artificial caries-like dentin lesions under severe demineralizing conditions was investigated. Bovine dentin samples (n = 180) were ground flat, polished, divided into four groups, and subjected to three demineralization cycles per day. Samples were stored in one of the following solutions for 5 min prior to demineralization in a buffer solution (pH 5): Group 1: 50% oil emulsion (olive oil and distilled water); group 2: 5% oil emulsion; group 3: distilled water; and group 4: 1,500 ppm sodium fluoride. Daily up to 9 days, lesion depth (ld) and mineral loss (ΔZ) were determined by means of microradiography and analyzed by ANOVA and Tukey’s studentized range test (p ≤ 0.05). Lesion depth increased with time for all groups. Mineral loss increased in groups 1–3. A small but significant decrease in mineral loss was observed following treatment with lipid emulsions as compared to treatment with distilled water, but fluoride treatment was considerably more effective. Mean mineral loss (means ± SD in vol%·µm) averaged over the study period was 4,368 ± 1,599, 4,536 ± 1,823, 4,849 ± 1,798, and 789 ± 177 for group 1, 2, 3, and 4, respectively. Ratio (ΔZ/ld) remained constant around 30 vol% for groups 1–3, but decreased for group 4. In conclusion, externally provided lipids have the potential to reduce dentin demineralization in vitro.