This paper examines the historical relationship between renewable energy intensity in South Korea (Korea) and major fuel prices with macroeconomic variables, and compares the results with the U.S. counterpart. Renewable energy initiatives have been more active in the world energy market since the Arab oil embargo in the early 1970s. South Korea, the 12th largest economy in 2018 and the 9th largest energy consumer in 2017 in the world, possesses little domestic natural resources and had to meet 98% of its energy needs from international sources. As renewable energy is a viable substitute for electricity generation, with biofuel for transportation energy use, renewable energy sources have well served South Korea and the U.S. The benefits have been two-fold: reduced dependence on foreign energy imports and the promotion of a cleaner environment. With renewable energy competing with fossil fuels for price advantages in energy markets, this paper analyzes annual data, from 1990 to 2017, to examine and identify the multifaceted relationship between fuel prices and renewable energy intensity, under the developing market dynamics in these countries. The implications will help engineering managers better understand sustainability issues under the dynamics of energy market systems.