In the method according to example embodiments, dynamic pressure oscillations in the inlet tract of the respective internal combustion engine are measured during normal operation, and from these a corresponding pressure oscillation signal is generated. A crankshaft phase angle signal is acquired at the same time. The pressure oscillation signal is used to determine an actual value of at least one characteristic of at least one selected signal frequency of the measured pressure oscillations in relation to the crankshaft phase angle signal, and the current compression ratio is determined on the basis of the determined actual value and using reference values of the corresponding characteristic of the respective same signal frequency for different compression ratios.