A new oxygenate additive for diesels (bio or petroleum) was manufactured using glycerol, dimethyl sulfate (DMS), and sodium hydroxide pellets as raw materials. By feeding the dimethyl sulfate into the batch reactor containing the sodium glycerate, a semibatch mode operation enhanced the effective methylation of glycerol. A conventional stirred tank reactor that can produce large quantities of oxygenate additives under a normal atmospheric pressure operation became the main feature of the methylation process. With a 3:2 molar ratio of DMS to glycerol, a 3:1 molar ratio of sodium hydroxide to glycerol, a 0.43:1 molar ratio of water to sodium hydroxide, and a temperature of 343 K at the reaction time of 24 h with the feeding time of DMS under 12 h,. the conversion of glycerol (93.5%) and a combined yield of GDMEs and GTME of 71.2% were achieved for a once-through operation. A product mixture of GDME (20 wt %) and GTME (80 wt %) served as a new oxygenate additive for (bio or petroleum) diesels.