Single-crystal Pt is well known to demonstrate oscillatory and complex dynamic behaviour, for instance, during the catalytic oxidation of CO. This type of behaviour is also observed for presently investigated supported Pt catalyst, EUROPT-3. In the present case self-oscillations have been examined during CO oxidation using in situ FTIR, applied to both steady-state experiments and step response, transient isotopic labelling and concentration programming experiments. The goal of the present investigation was to establish the feedback mechanism that is essential in explaining complex dynamic behaviour and to apply periodic operation to suppress the self-oscillations. For low CO/O-2 ratios the reaction demonstrates so-called regime I kinetic behaviour with reaction orders in CO and O-2 being, respectively, one and zero. Platinum is slowly oxidised, thereby blocking sites for adsorption and subsequent reaction. At a critical point, corresponding to a degree of oxidation of the Pt of approximately 61%, regime II type behaviour is observed: the system exhibits multiplicity and self-oscillations. With progressing oxidation of Pt both the period and the amplitude of the oscillations increase. Although the existence of oxidised Pt seems to be correlated to the emergence of self-oscillations, quantitative analysis of the oxidation and reduction kinetics of Pt reveals that the dynamics of these reaction steps are at least two orders of magnitude too slow to act as feedback mechanism. A qualitative comparison of other known feedback mechanisms indicates that a phase transition mechanism can describe the observed self-oscillations. It is shown that forced concentration oscillations suppress the self-oscillations. Periodic reduction of the catalyst in CO is effective in keeping the amount of oxidised Pt low, and thereby prevents the system from entering regime II.