Since 1939, drinkers of Rolling Rock beer have wondered why the number '33' was chosen for the back of the bottle.

There are various speculations:

- Prohibition was repealed in 1933.
- There are 33 words in the Rolling Rock Pledge (including 'Rolling Rock').
- 33 letters compose the ingredients: water, malt, rice, hops, corn, brewers' yeast.
- The '33' was used in typesetting to signify the end of a document. It was an accident that it appeared on the first batch of bottles. Apparently it was too expensive to have them removed, so the '33' stuck.
- 33 was the union's local number for workers at the brewery.

None of these have been verified by Rolling Rock.