In most houses with a natural gas line, the main shut-off valve is usually located just before the gas meter. Also known as the street-side valve, this valve is normally a simple rectangular nub. The house-side valve is a ball valve and is located farther down the gas line.
When the long side of the rectangular nub on the street-side valve is parallel to the supply pipe, the line is open and gas is flowing. When the nub is turned perpendicular to the pipe, the valve is shut and the gas supply is cut off. The house-side valve is farther down the gas line and only controls the gas flow to particular fixtures, not the entire gas supply.