A method for determining and/or monitoring at least one measured variable of an at least partially gaseous medium with at least one mechanically oscillatable unit, which is excited to execute mechanical oscillations, and whose mechanical oscillations are received and evaluated. At least one characteristic curve is stored, which describes for at least one gas or a gas mixture at least the dependence of at least one characteristic variable of the mechanical oscillations of the mechanically oscillatable unit on pressure; at least the characteristic variable of the mechanical oscillations of the mechanically oscillatable unit is determined; the determined characteristic variable is compared with the stored characteristic curve; and, starting from the comparison of the determined characteristic variable with the stored characteristic curve, the measured variable of the medium is determined. Further, an apparatus for determining and/or monitoring the measured variable is envisioned.