Natural gas is found, produced, and transported under pressure. The only time natural is at atmospheric pressure is generally if it leaks into the atmosphere.
The mass number of moles do not change regardless of the pressure (or temperature) of the system. However, industry uses volumes in trading which can lead to confusion as transport, vessels, etc can be a t a variety of temperatures, pressures, and volumes.
As a result, industry always reports the equivalent volume at standard conditions.
Some typical standard values for standard pressure and temperature are:
Pst = 14.7 psia
Tst = 60 F