First episode: August 2, 1971
Last episode: June 28, 1974
Seen weekday afternoons 1:30-2:00 on NBC
Players bid against each other to answer true-false questions and accumulate money. The money was used on the game board, where they "bought" boxes and tried to match items in three columns. The rules for the main game changed in the final few months (around March, 1974), plus producer Bob Stewart was constantly adding bonuses and extra features, but the game stayed essentially the same.
Read a negative Hollywood Reporter review from August 6, 1971.
Game show fans who are old enough remember this show fondly, but at the time it was about as insignificant a game as ever enjoyed a three year run.  The repetitive play did lend itself to familiar catch phrases.  To a fan, "That's true, Bill" or "I'll take $40 on the red" were as identifiable then as "I'd like to buy a vowel" is today.

The format of Three on a Match changed on April 23, 1973 to a game where the contestants matched images on the game board instead of prizes.  One of the most popular sets of images used were faces from classic horror films -- along with Bill's own smiling press photo, doctored to resemble a devil.
As he did earlier with Eye Guess, Bill held the reins loosely.  He could often be found joking around with the unseen stagehand operating the category board.  Knocking on the wall behind him appeared to be a good luck standard at the start of each show as well.
During the week of November 12-16, 1973, Three on a Match was among the daytime game shows that participated in something called the NBC Celebrity Holiday Festival for Children. During that week, Fannie Flagg, Bernadette Peters and Soupy Sales played the game for charity.

Bill earned the first of his three Emmy nominations for Three On A Match, though many reference books fail to mention it.  The nomination came for the 1972-73 season, one year before the television academy established a separate Daytime Emmy Awards.

At that time, the academy recognized a wide variety of programming -- including daytime, sports and childrens shows -- in a group of categories called "The Areas".  Programs and individuals received nominations in various "areas", and there was the possibility of multiple winners, or no winner at all, in each category.  Bill was nominated, along with Peter Marshall and Paul Lynde of Hollywood Squares, for "Achievement by Individuals in Daytime Programming", which the academy defined as "an award for individual achievements which do not qualify in daytime drama."  None of the performers received an award that year. Bill would later be nominated for Emmy Awards for his work on Blockbusters and Hot Potato.

Three on a Match
aired for the last time on a Friday.  The following Monday, Bill could be seen hosting a new Bob Stewart game, Winning Streak.  
Larry Blyden (another Bob Stewart favorite) once substituted for Bill as host of Three on a Match.
A small handful of episodes are traded among collectors.  There are also five episodes from March-April, 1973 in the UCLA archives, but they are currently not available for viewing.
Watch the opening minutes of the 3/15/73 episode:  

The Three on a Match page at Adam Nedeff's Bill Cullen's World
The Three on a Match page on Wikipedia
The Three on a Match page at Tim's TV Showcase