Lactones, cyclic esters of hydroxycarboxylic acids, are interesting biofuel candidates as they can be made from cellulosic biomass and have favorable physical and chemical properties for distribution and use. The reactions of gamma-valerolactone (GVL), gamma-crotonolactone (2(5H)-F), and alpha-methyl-gamma-crotonolactone (3M-2(5H)-F) with Cl, OD, and O-3 were investigated in a static chamber at 700 Torr and 298 2 K. The relative rate method was used to determine k(GVL+Cl) = (4.56 0.51) x 10(-11), k(GVL+OD) = (2.94 0.41) x 10(-11), k(2(5H)-F+Cl) = (2.94 0.41) x 1011, k(2(5H)-F+OD) = (4.06 0.073) x 10(,)(-12) k(3M-2(5H)-F+Cl) = (16.1 1.8) x 10(-11), and k(3M-2(5H)-F+OD) = (12.6 0.52) x 10(-12), all rate coefficients in units of cm3 molecule(-1) s(-1). An absolute rate method was used to determine k2(5H)-F+O-3 = (6.73 0.18) x 10(-20) and k(3M-2(5H)-F+O3) = (5.42 1.23) x 10(-19) in units of cm(3) molecule(-1) s(-1). Products were identified for reactions of the lactones with Cl. In the presence of O-2 the products are formic acid (HCOOH), formyl chloride (CHClO), and phosgene (CCl2O), and also maleic anhydride (C2H2(CO)(2)O) for 2(5H)-F. In addition both reactions produced a number of unidentified products that likely belong to molecules with the ring-structure intact. A review of literature data for reactions of other furans show that the reactivity of the lactones are generally lower compared to that of corresponding compounds without the carbonyl group.