Arsenal took the lead just after the half hour mark when Oxlade-Chamberlain found the bottom corner of Al-Habsi's goal with a drilled effort .
Reading had a good chance to equalize through Callum Harriot, but the Reading man's deflected effort looped just over the bar.
On 78 minutes, Oxlade-Chamberlain made it 2-0 when his deflected shot found the net.
Reading didn't make life easy for Arsenal and acquitted themselves well for most of the game, but it was always going to be an uphill struggle once Arsenal had opened the scoring.
Arsenal will now go into the draw for the quarter final which shall be made after the Manchester derby on Wednesday night.