The paper presents a series of 48 enclosure fire experiments carried out in a m cubic compartment with a door-like opening of m width and a variable height from 0.25 to m. The fire source was a propane-fueled square burner of m side length positioned in the center of the compartment and delivering a steady mass flux that has been varied in the tests from 0.5 to g/s. In addition to the well-known well-ventilated and under-ventilated regimes, an oscillatory combustion regime has been uncovered for an opening height of 0.25 or m. This regime is characterized by an alternation between the well-ventilated regime (combustion exclusively inside the compartment) and the under-ventilated regime (combustion inside and outside the enclosure). It is believed that the time for the onset of the oscillations is linked to the smoke filling time. Furthermore, depending on the specific conditions, the oscillations are either steady (until shut-off of the fuel supply) or transitory (leading to a sustained under-ventilated regime). The frequencies ranged from about 9 to mHz. The oscillatory regime has previously been mainly reported for liquid fuels and thus associated to radiative heat feedback effects. The new data for a gaseous fuel calls upon a better understanding and a further analysis of the underlying physics.