A method and a device for optically determining state variables inside a container (1) for liquefied gases. In the method and device, light emitted by an illumination unit (2) travels within an optical waveguide (7, 9) to a contact point (33) with the content of the container (1) and is partially reflected there, the intensity of the reflected light is measured by an image sensor (4), and a state variable is determined from the intensity. In order to create a comprehensive “image” of the state variables in the container and of the container content, several optical waveguides (29, 29′) are guided to contact points (33) which are distributed within the container (1) and form measurement points (9.1, 9.2, 9.3, . . . , 9.n). Locally assigned state variables (refractive index, density, temperature, etc.) of the container content are determined from the measured values obtained at the measurement points (9.1, 9.2, 9.3, . . . , 9.n) and are evaluated along with the spatial coordinates of the measurement points (9.1, 9.2, 9.3, . . . , 9.n) in the container (1).