Energy systems, and the technologies that support them change over time. There have been a number of changes in US energy consumption over the past 200 years. Overall consumption has gone up, and the sources of energy have varied considerably. Until the late 1800s, renewables (biomassBiomass) were the largest energy source. CoalCoal became until the late 1940s, when petroleum overtook coalCoal. Natural gasNatural gas has increased since the early 1900s, rivaling petroleum by 2020. Recently, petroleum consumption and nuclear power have plateaued, and coalCoal consumption has decreased. We can expect changes in energy resources in the future as well.