A method and apparatus are provided for compressing vertex parameter data in a 3D computer graphic system, where the vertex parameter data is a data block relating to a plurality of vertices used for rendering an image. The data relating to each vertex includes multiple byte data relating to at least one parameter. The parameters include X, Y and Z coordinates and further coordinates for texturing and shading. The multiple byte data is divided into individual bytes and bytes with corresponding byte positions relating to each vertex are grouped together to form a plurality of byte blocks.