Electric distribution companies regulation has important effect on power system. Distribution services costing are done by two method, price base and performance base. Distribution company cost include operational and investment. Services quality, productivity improvement and etc are applied by benchmarking. With regard to different condition of companies, it is important that regulator benchmarks similar of them.

In this paper, comprehensive algorithm is proposed to distribution companies clustering in operation expenditure (Opex) determination process. Three method and different cluster validation indexes is used in clustering that increase accuracy. Subsequently, clustering methods effects analyses in opex by standard deviation index. Finally proposed method is applied to UK electric distribution companies.