What is the only state in the US where you can't pump your own gas?

New Jersey. Full service only.

https://www.cbsnews.com/miami/news/theres-only-one-state-left-where-its-illegal-to-pump-your-own-gas/

The only state in the United States where you cannot pump your own gas is New Jersey. Since 1949, a state law known as the Retail Gasoline Dispensing Safety Act has prohibited self-service gas stations. The primary reasons cited for the law include safety concerns, preserving jobs for gas station attendants, and convenience for customers.

Although Oregon previously had similar restrictions, the state changed its rules in 2023 to allow self-service throughout the state. This left New Jersey as the only state with a complete ban on self-pumping.

https://www.nj.gov/labor/safetyandhealth/resources-support/laws-regulations/gasact.shtml