Gallagher was the fastest of the 40 drivers that took to the two-mile, high-speed track, clocking in a speed of 190.305 mph. Reed was second-fastest at 190.119 mph.
Elliott Sadler was fifth-fastest (189.459), followed by Brennan Poole (189.334), William Byron and Cole Custer (tied for seventh-fastest at 188.971 mph), Cup regular Denny Hamlin (188.952) and Brandon Jones (188.897).
The second and final Xfinity practice takes place later this afternoon from 3 to 3:55 p.m. ET.