Turkey's demand for energy has been rapidly increasing as a result of factors like industrialization, urbanization and rapid population growth. In meeting the increased demand, the efficient utilization of energy in all Turkish sectors plays an essential role. The present study, consisting of two parts, analyzes sectoral energy utilization in Turkey over an 11-yr period from 1990 to 2000. In order to calculate sectoral energy utilization efficiency values, Turkey is subgrouped into four main sectors, namely, utility, industrial, transportation, and commercial-residential. Part 1 of this study investigates the first two subsectors, while the remainder is treated in Part 2, where all the sectors considered are discussed in detail. Turkey's overall first law efficiencies for the entire utility sector are found to vary from 30.10 to 35.21%, while those for the whole industrial sector are obtained to range from 61.20 to 68.97%, with average values of 31.82 and 63.57%, respectively. It is anticipated that the present study will provide useful insights into the Turkish energy use and the planned studies towards increasing energy efficiencies in the sectors studied.