What a thrill to see the Mariners clinch their sixth playoff appearance! Fans know it is rare. But fans of many teams gripe about lack of postseason success. How rare is it for the M's? I used franchise histories from baseball-reference.com to put numbers to it.

This source tracks franchises, so, for example, the Washington Nationals and Montreal Expos are one franchise with a 57-year history. The Minnesota Twins, 1957-1961 Washington Senators, 1905-1957 Washington Nationals, and 1901-1905 Washington Senators are one franchise with a 125-year history.  

Since the 2025 playoff picture is still incomplete, I've excluded it.

The Chicago White Sox made the playoffs in only 8.8% of their 125 seasons. Ouch. That makes them the most maybe-next-year team in MLB. And the Mariners are second. Prior to 2025 the M's only made the playoffs in 10.2% of their 49 seasons. Other teams with among the lowest rates of making the postseason include the Washington Nationals, the Cincinnati Reds, and the Pittsburgh Pirates. 

Factor in number of penants won and number of championships won and the Mariners fans have a strong case to make for experiencing the least glory. Many White Sox fans are old enough to remember the 4-0 World Series sweep in 2005 behind that solid pitching rotation. M's fans not only lack a winning-it-all experience like that, we also lack any experience of the World Series whatsoever. And the M's are the only team in Major League Baseball to never have made it to a World Series.

By making the 2025 playoffs the M's might leapfrog a few spots in the rankings by percent of seasons that include postseason action. And it means they have a shot to change more than that. That's so fun and exciting and will keep this fan rooting for them for years to come.