In this article, the problems of unbiased estimation of parameters in linear and quadratic mixture models have been revisited. We have studied some standard mixture designs for this purpose. The information matrices of the parameters involved in the linear and quadratic mixture models have been displayed for these standard designs. Some generalizations of the axial designs have been proposed and a comparative study of these designs, in respect of their information matrices, has been considered. Other types of mixture models viz. Becker's homogeneous model and Draper - St. John's model have also been briefly studied and the estimation problems have been addressed by using some axial type designs. © 2010 Pakistan Journal of Statistics.