The rearrangement of 3-methyl-2-oxetanone ( lactone) into methacrylic acid has been explored using DFT methods. Calculations were performed for (i) intramolecular, (ii) lactone-lactone and (iii) water and phosphomolybdic acid catalyzed conversions. The water and acid surface catalyzed route exhibited the lowest activation barrier ( 156 kJ mol(-1)) of the three reaction pathways and overall is slightly endothermic (Delta H-f = 37 kJ mol(-1)).