TSA classifies peanut butter as a liquid.

The Transportation Security Administration (TSA) considers peanut butter a liquid due to its lack of definite shape and has a carry-on quantity limit of 3.4 ounces per passenger. Travelers have reported conflicting experiences with TSA officers citing the rule for other non-peanut-butter items. The final decision on whether an item is allowed through the checkpoint rests with the TSA officer. It is recommended to check the "What Can I Bring?" page on the TSA website before packing carry-on bags.