Does Pv=nRT use gauge pressure or absolute pressure?

Absolute pressure. Same stuff happens with T which is the absolute thermodynamic temperature, neither in degrees Celsius nor in Fahrenheit as the 0 point for these temperature scales is arbitrary. read more

A welder using a tank of volume 7.70×10^−2m^3 fills it with oxygen (with a molar mass of 32.0 ) at a gauge pressure of 3.30×10^5 Pa and temperature of 35.0 C. The tank has a small leak, and in time some of the oxygen leaks out. read more

Absolute pressure is zero-referenced against a perfect vacuum, so it is equal to gauge pressure plus atmospheric pressure. Gauge pressure is zero-referenced against ambient air pressure, so it is equal to absolute pressure minus atmospheric pressure. read more