This chapter provides a survey of studies concerning the relationship between crude oil prices and other energy commodities such as coal and natural gas. Although such an assessment demands an interdisciplinary approach to provide readers with important background information, the approach taken here is based upon the economics of the energy market. The empirical studies summarized here can be categorized into three groups: time series studies analyzing market integration between oil and other energy commodities, studies that examine the predictive content of futures prices for energy, and the role of tail risk in explaining price volatilities of oil and other energy commodities. Several suggestions for future research are offered.