This thesis investigates the topic of subsurface reservoir grid visualization. An open-source Matlab toolbox for simulating and visualizing reservoirs is introduced. To make this toolbox work in Octave, an open-source Matlab clone, it is necessary to improve Octave’s visualization. This is done by implementing two new visualization functions, which can be used from Octave. The first method tries to offer the same functionality as Matlab, but better performance, by improving an Octave function. The goal of the second method is to offer more advanced visualization, by fully utilizing the graphics processing unit and modern rendering techniques. The methods are tested, and compared to Matlab and standard Octave. It is shown that the new methods accomplish what they aim to do, and it is concluded that by doing as much work as possible on the GPU, we get higher performance and open up for more advanced visualization of subsurface reservoirs.