We show that introduction of an additional adsorbate with appropriate adsorption and desorption rates leads to sustained oscillations in the CO oxidation on a catalytic surface. The adsorbate does not participate in the formation of CO2, but only blocks sites. We speculate on the possibility of experimental verification of our results by calculating the properties that the extra adsorbate should have. We have studied the reactions using a master equation that we have solved with the dynamical Monte Carlo method, using macroscopic rate equations, and using a combination of these two.