This paper deals with problems related to determination of customer costs of reliability – the total amount of costs related with power supply interruptions (loss of production, overtime costs to personnel (stuff), etc.) and expenses related with activities for diminishing negative effect of power supply interruptions (UPS devices, generators, additional insurance, etc.). The paper gives description of different cost estimation methods based on review and analysis of proposals for customer cost estimation and customer cost estimation surveys from different countries. On the basis of analysis of different customer cost estimation surveys and questionnaires, there is proposed new design of questionnaire for surveys with the aim to use it for performing customer cost evaluation study in the frames of “Government action plan” of Latvian government for year 2012. Problem of survey data normalization is discussed and proposal of appropriate normalisation factors, from authors` point of view, is given. Results of the work presented in the paper could be used when: • trying to get knowledge of customer valuation of reliability; • developing financial incentives for performance-based regulation of utilities (system operators); • developing guaranteed reliability standards; • etc.