Simplified chemical pathway for the formation of methyl formate and its isotopologues on the ice surface of dust grains. Species enclosed in a black box have been observed in the ISM. Normal arrows represent addition reactions, and hydrogenation when there is no radical noted near by, dashed lines are for H–D substitution, double-headed arrows show abstraction + addition reactions, and thunderbolt arrows represent photodissociation reactions. D-atom addition reactions are represented in red. This is a compilation of the studies of Garrod & Herbst (2006), Hidaka et al. (2009), and Taquet et al. (2014).