抄録
Japan's self-sufficiency rate of energy is a mere 4%, the lowest among the developed countries. In order to improve the low
self-sufficiency rate, the development of renewable energy is recommended as a promising means to contribute to long-term
energy supply. However, according to the government's forecasting its contribution to energy mix in 2030 is estimated about
11%. The other way to prevent economical risks from low self-sufficiency rate is to diversify import areas for supply sources.
However, the market supplied by the lowest price does not always give security for stable supply. It is important to clarify
quantitatively the minimum of economical risk by using past data of imported fossil fuels, especially crude oil which has the
highest volatility of fuel price. In this paper, we focus on the economical risk of imported crude oil and propose the method to
analyze the source distribution of imported fossil fuels by applying portfolio theory developed by Markowitz. We then apply
the method to the past data sets of five high risk terms and three low risk terms and analyze the characteristics of the past
crude oil markets in Japan.
