Choosing to play with the Flames, Vail made his NHL debut in 1973–74, appearing in 23 games. He scored two goals and nine assists, but spent the majority of the season in the Central Hockey League (CHL) with the Omaha Knights. Since he played fewer than 25 NHL games in his first season, Vail was still considered a rookie in 1974–75. He led all rookies with 39 goals and had 60 points on the campaign. Vail won the Calder Memorial Trophy as the NHL's rookie of the year, the first player in Flames history to do so.