1984 Cutlass Supreme - Gas tank pressure

[Azucho98]

Is it normal for a 1984 Cutlass Supreme with a 307 V8 to build pressure in the gas tank? Filled up today, gas was running quite low. It took a while for the pressure in the gas tank to release once I loosened the gas cap. The car is as stock as it gets, all emissions stuff still attached.

Thoughts on this?

Thanks in advance!