A pulsed laser photolysis-photoionization mass spectrometer system has been employed to measure the rate constants of HCCO + O-2 and HCCCO + O-2 over the temperature range 243-423 K in 1.2-8.4 Torr of He or N-2. Radicals of HCCO and HCCCO were produced by 193 nm ArF laser photolysis of ethyl ethynyl ether and methyl propiolate, respectively. HCCO was photoionized by a Kr resonance lamp with a CaF2 window (10.03 eV), and HCCCO was ionized by a Xe lamp with a sapphire window (8.44 eV). Both ions were detected as parent ions in a quadrupole mass spectrometer. From analysis of the time profiles of the ion signals for various O-2 concentrations, the overall rate constants at 298 K are represented by the values k(2) = (6.3 +/- 1.0) x 10(-13) for HCCO + O-2 and k(5) = (5.7 +/- 0.6) x 10(-12) for HCCCO + O-2 in the units cm(3) molecule(-1) s(-1). The rate coefficients for the two reactions can be described by k(2) (T) = (1.5(-0.7)(+1.5)) x 10(-)(12) exp[-(225 +/- 220)/T] and k(5) (T) = (1.8(-0.9)(+1.9)) x 10(-12) exp[(343 +/- 228)/T] in the units cm(3) molecule(-1) s(-1) over the temperature range 243-423 K.