Despite significant time- and cost-reductions, the online survey method has to cope with important methodological problems, which are mainly related to the lack of representativeness of the results.  This is especially the case for online access panel surveys.  Therefore, the main question that will be addressed is how representative online survey data are for the general public.  Based on recent figures of the European Social Survey, it seems that important differences in demographic characteristics still exist between people who have internet access and who haven’t.  As a possible solution to reduce possible biases of unrepresentative web surveys, it has been suggested to apply post-stratification weights (to adjust for demographic under- and over-representations in the sample) and, more recently, to use propensity-score adjustments (to correct for differences due to the varying inclination to participate in online panel surveys).  The impact of these frequently applied weighting techniques on the representativeness of online survey results was evaluated by conducting a comparison study between an online panel survey and a random reference survey.  It was found that these weighting techniques not necessarily make substantive answers to attitude questions (e.g. about politics, work satisfaction, ethnocentrism) similar to those of the general population.