Methylene glycolate (MG) and methyl methoxyacetate (MMAc) were synthesized from formaldehyde and methyl formate (MF) mixtures heated to 150°C for 3 hr using silicotungstic acid as the catalyst. Methanol was added to stabilize the formaldehyde. Dimethoxymethane (DMM) and dimethyl ether were the major byproducts. MG and MMAc yields were limited by the slow release of CO from MF, but the yields of these products could be increased significantly by adding a small amount of gaseous CO. Carbonylation of DMM as a formaldehyde source was achieved with both MF and gaseous CO. MG and MMAc yields were generally higher with DMM than with formaldehyde, with a greater selectivity for MMAc than MG. A comparison of common heteropoly acids showed that SiW12 had the greatest combined MG and MMAc yield, followed by phosphotungstic acid. Silico- and phosphomolybdic acids were much less active, mainly due to their reduction leading to deactivation. This is an abstract of a paper presented at the 2007 AIChE Annual Meeting (Salt Lake City, UT 11/4-9/2007).