A method for preparing methyl methacrylate from methacrolein and methanol. The method comprises contacting in a reactor a mixture comprising methacrolein, methanol and oxygen with a heterogeneous catalyst comprising a support and a noble metal, wherein said catalyst has an average diameter of at least 200 microns, wherein oxygen concentration at a reactor outlet is from 0.5 to 7.5 mol % and wherein the reactor comprises a partition with the catalyst bed on a first side of the partition and with flow through the catalyst bed in a first direction and flow on a second side of the partition in an opposite direction.