The invention relates to methods of determining whether a wellbore sealing operation has been performed correctly, and to wellbore-lining tubing which facilitates the determination of whether a wellbore sealing operation has been performed correctly. The invention has a utility in determining whether cement has been correctly supplied into an annular region defined between an internal wall of a wellbore and an external surface of a wellbore-lining tubing located in the wellbore, or whether a packer has been properly set to seal such an annular region. One disclosed method comprises the steps of: locating a wellbore-lining tubing (140) in a wellbore (100), said tubing having at least one pressure sensor (80); performing a wellbore sealing operation in an annular region (178) defined between an external surface of said tubing and an internal surface (130) of a wall of the wellbore, or between an external surface of said tubing and an internal surface of another wellbore-lining tubing (118) in which said tubing is located, to seal said tubing in the wellbore; monitoring the pressure of fluid in the annular region using the at least one pressure sensor; and recovering data concerning the pressure of the fluid monitored by the sensor to surface, the pressure data indicating whether the wellbore sealing operation has been performed correctly.