O-methyltransferase that modifies the hydroxy group of the fatty acids. Oleate is the most effective fatty acid acceptor. a fatty acid + S-adenosyl-L-methionine = a fatty acid methyl ester + S-adenosyl-L-homocysteine Cells are unable to methylate the glycopeptidolipid fatty acids. Belongs to the methyltransferase superfamily. Truncated N-terminus.