Preserving Foods in Oil
Garlic, vegetable or herb in oil mixtures may support the growth of C. botulinum bacteria. At least three outbreaks of botulism associated with garlic-in-oil mixtures have been reported in North America. For safety reasons, they should be made fresh. Leftovers should be frozen, refrigerated for use within 10 days, or discarded. Do not store at room temperature. Peeled garlic cloves may be submerged in oil and stored in the freezer for several months.
University of California - Davis
Colorado State University