https://www.mercurynews.com/2022/03/22/tips-for-fending-off-gas-thieves-include-locking-gas-caps-and-more-roadshow/

Q: I had a full tank of gas the other night and discovered the next day, while driving on the freeway, that it was empty. Thieves had siphoned all the petrol from my SUV. Thank God there was a gas station close to the San Jose airport.

I paid $59.24 for 10 gallons of gas, which filled half my tank. Needless to say, we purchased a locking gas cap right away.