This invention comprises a system for measurement of temperature and pressure in oil wells. It comprises a single hybrid mandrel housing a pressure and temperature double optical sensor, capable of measuring temperature and pressure both in the ring and in the production tubing of an oil well and an insertable venturi tube inserted in the direction of a pressure differential optical sensor, capable of taking flow rate measurements, the installation aspects of which are substantially simplified. With the proposed construction, it is possible for one single hybrid mandrel (30) to read the pressure and temperature in the ring and tubing and the flow rate. With this, changes of flow rate are also possible, without the need to stop production for long periods for the hybrid mandrel (30) to be replaced, the mere replacement of the insertable venturi (12) sufficing, by means of an insertion and extraction tool (17), which is an operation requiring a much shorter time.