Draft:NHL playoff ties

Except for 1920, the NHL has always used a playoff tournament to determine its champion. The league's playoff system has changed over the years, from the NHL's inception in 1917, to when the NHL took over the Cup in 1926, to the current setup today.

Current rules require overtime for playoff games that are tied after regulation, however that was not always the case. Game 4 of the 1988 Stanley Cup finals between the Edmonton Oilers and the Boston Bruins was abandoned after 36:37 of play, but this game is not considered official except for player statistics.

Starting in 1915, the Cup was officially contested between the champion of the National Hockey Association (NHA) and the champion of the Pacific Coast Hockey Association (PCHA). After a series of league mergers and folds, including the 1917 establishment of the NHL as a successor to the NHA, the Stanley Cup became the championship trophy of the NHL prior to the 1926–27 season, so in this period, there were Stanley Cup Finals games between the NHL and other leagues during this period.

Emergence of the NHL
The National Hockey League (NHL) was founded in November 1917 as a successor to the NHA. From the NHL's inception until 1920, both NHL and PCHA teams were eligible for the Stanley Cup. The NHL finals was a two-game total goals series in 1918 and a best-of-seven series in 1919. In 1920, the Ottawa Senators were automatically declared the league champion when the team had won both halves of the regular season. The two halves format was abandoned the next year, and the top two teams faced off for the NHL championship in a two-game total goals series.

At the time, the NHL champion would later face the winners of the PCHA and, from 1921, the Western Canada Hockey League (WCHL) in further rounds in order to determine the Stanley Cup champion. During this time, as the rules of the NHL and those of the western leagues differ (the main difference being that NHL rules allowed five skaters while the western leagues allowed six), the rules for each game in the Stanley Cup Finals alternated between those of the NHL and the western leagues. Before the WCHL competed for the Stanley Cup, the Cup championship series was a best-of-five series. Following the involvement of the WCHL, one league champion was given a bye straight to the finals (a best-of-three affair starting in 1922), while the other two competed in a best-of-three semifinal. As travel expenses were high during these times, it was often the case that the NHL champions were sent west to compete. In a dispute between the leagues in 1923 about whether to send one or both western league champions east, the winner of the PCHA/WCHL series would proceed to the Stanley Cup Finals, while the loser of the series would face the NHL champion, both series being best-of-three.

In 1924, the NHL playoffs expanded from two to three teams (with the top team getting a bye to the two-game total goal NHL finals), but because the first-place Hamilton Tigers refused to play under this format, the second and third place teams played for the NHL championship in a two-game total goals affair. The Stanley Cup Finals series returned to a best-of-five format the same year.

NHL takes control of Stanley Cup
With the merger of the PCHA and WCHL in 1925 and the merged league's collapse in 1926, the NHL took de facto control of the Stanley Cup. While the Cup would not be formally deeded to the league until 1947, from 1926 onward the NHL playoffs and the Stanley Cup playoffs are considered synonymous. The NHL was subsequently divided into the Canadian and American divisions for the 1927–28 season. For 1927, six teams qualified for the playoffs, three from each division, with the division semifinals and finals being a two-game total goals affair, and the Stanley Cup Finals becoming a best-of-five series. 1927 also saw the introduction of overtime and a reduction in the number of potential ties in "best of" series. In 1928, the playoff format was changed so that the two teams with identical division ranking would face each other (i.e., the division winners played each other, the second place teams play each other, and likewise for the third place teams). The first place series was a best-of-five affair, with the winner proceeding to the best-of-three Stanley Cup Finals, while the others were a two-game total goals series. The winner of the second and third place series played each other in a best-of-three series, with the winner earning the other berth to the Stanley Cup Finals. This format had a slight modification the following year, where the semifinal series became a two-game total goals affair and the Stanley Cup Finals became a best-of-five series. The two-game total goals format was abolished in 1937, with those series being changed to best-of-three affairs.

The 1951 playoffs saw the last tie in NHL playoff history when the Boston Bruins and the Toronto Maple Leafs ended game 2 of the Stanley Cup final ahead of the Sunday curfew in Toronto.