[en] This paper estimates hydrothermal exploration costs and the effects that using slim holes could have on those costs using a computer code developed for the US-DOE. The primary goal of exploration is to generate decision driving information about particular geothermal reservoirs. Compared to today's exploration strategies, the main effect of using slim holes would be to reduce the cost of exploration by about 40 percent. Slim hole exploration does not reduce the overall cost of electricity by much; however, the cost burden is shifted later in the project when outside financing is more likely. The reduced costs of slim holes may also encourage developers to drill more holes that better characterize the reservoir, thus reducing long term reservoir risk. The cost of power could then be cut as much as six percent and project financial risks related to reservoir uncertainties could be reduced by up to one quarter. In order to realize these improvements, the amount of reservoir information recovered from small diameter bore holes needs to be significantly increased