The kinetics of n-pentane oxidn. over a (VO)2P2O7 catalyst is described by a Langmuir-Hinshelwood mechanism: four parallel reactions leading to maleic anhydride, phthalic anhydride, CO, and CO2; and two consecutive reactions for the formation of C oxides from the two anhydrides. The rate-detg. step is a surface reaction between one adsorbed n-pentane mol. and one O mol., indicating that the reaction leading to C-C bond formation in phthalic anhydride synthesis occurs after the rate-detg. step. Phthalic anhydride selectivity is higher for the lower reaction temps. and n-pentane or O concns. The relevance of the kinetic information with regard to the anal. of the mechanism for the formation of the C8 anhydride from the C5 alkane is also discussed. [on SciFinder(R)]