 He was then drafted in the first round, fifth overall, by the Colorado Rockies in the 1978 NHL Entry Draft.In the 1978–79 season, Gillis played two games with the Philadelphia Firebirds of the American Hockey League (AHL), scoring no points; he also spent 30 games with the Rockies, earning eight points (one goal and seven assists).He split the 1979–80 season with the Rockies, scoring four goals and five assists in 40 games, and the Fort Worth Texans of the CHL, with 22 points (nine goals and 13 assists) in 29 games.