Involved in glycerolipid synthesis and lipid metabolism. Catalyzes the formation of diacylglycerol, the precursor of triacylglycerol, by transferring the acyl chain of a fatty acyl-CoA to a monoacylglycerol, mainly at the sn-1 or sn-3 positions. It uses both sn-2-monoacylglycerol (2-acylglycerol) and sn-1-monoacylglycerol (1- acyl-sn-glycerol) equally well as substrates, and uses sn-3- monoacylglycerol (3-acyl-sn-glycerol) with lower efficiency. Probably not involved in absorption of dietary fat in the small intestine. . This is the function of MOGAT1 (monoacylglycerol O-acyltransferase 1, ENSG00000124003).