Policymakers in the US and around the world are grappling with how to understand the security implications of an energy system in transition—and if they aren’t, they should be. Recent attacks on Saudi facilities show that oil supply remains vulnerable to disruption. New energy forms can help reduce vulnerability to oil supply outages, but they also have the potential to introduce new vulnerabilities and risks. The US and its allies have spent the past 50 years building a robust domestic and international response system to mitigate risks to oil supplies, but similar arrangements for other energy forms remain limited. This paper offers a framework for assessing energy security based on an evaluation of vulnerability, risk, and offsets; this approach has been a useful tool for assessing oil security for the past 50 years, and it can be relevant for assessing energy security in an energy system in transition.