There are two kinds of gases inside our stomach: gas from our mouth and gas produced inside the intestines.
These gases will either be absorbed by the blood or discharged outside the human body by means of hiccup or flatulence.
In general, the volume of gas entered into the stomach from inhalation (or produced in the intestines) and the gas discharged outside the body will maintain a balance.
In a balanced state, the stomach will have about 200ml (about one glass) of gas.

The gas inside the stomach comes from inhalation or is produced during the neutralization of the gastric juice and pancreatic juice and by the bacteria inside the intestines.
Gas entered into the stomach from inhalation (or produced in the intestines) will normally be absorbed by the blood and released via the lungs. Gas discharged from hiccups or flatulence is less than 10%.

In general, the stomach will maintain a balance between the gas inside and the gas discharged. If the balance failed, the gas inside the stomach will accumulate and the stomach will begin to distend or rumble. In this case, we will feel discomfort or stomach distention.
Gas deposits inside the stomach for two reasons.
There is too much gas entered into (produced in) the stomach or there is too little gas discharged from the stomach.