An invert oil-based mud (OBM) may include an oleaginous continuous phase, an aqueous internal phase, and an emulsifier. The emulsifier may include one or more of the group consisting of epoxidized methyl oleate, epoxidized methyl linoleate, and epoxidized methyl α-linolenate. The invert OBM may contain the emulsifier in an amount of the range of 0.1 to 10 wt. % (weight percent), relative to the total weight of the OBM.