The present invention relates to a process for preparing carboxylic acid esters, comprising the reaction of at least one primary monoalcohol or of a mixture of a primary monoalcohol and at least one alcohol different therefrom in the presence of a transition metal carbene complex catalyst K which has, as central atom M, at least one transition metal atom of group 8, 9 or 10 of the Periodic Table of the Elements (IUPAC) and at least one monodentate N-heterocyclic carbene ligand, in the presence of a base, wherein the catalyst K is prepared by reacting a transition metal compound V which has at least one transition metal atom of group 8, 9 or 10 of the Periodic Table of the Elements (IUPAC), but no carbene ligand, with an imidazolium salt in the presence of the primary monoalcohol and the base, the reaction being carried out without dilution.