Hi Doug. Our Golf Ball R&D team answered this question earlier this year in a Team Titleist Q&A:

TT: Nathan S. asks, “What is the predictable shelf life (of a Titleist golf ball)?”

R&D: Today's Titleist golf balls can be safely stored for five years or even more, as long as they're kept away from excessive heat. Attics and cars, for example, can get very hot during the summer and can dramatically shorten a ball's life. Normal indoor conditions should be fine for storage.

One thing to consider though is that golf ball technology is improving rapidly and we are continuously raising the bar, so if you're playing balls that were made more than a couple of years ago, you may be missing out on some significant improvements that have been made to that model.

You can read the rest of the interview at this link: http://www.titleist.com/teamtitleist/b/tourblog/archive/2011/03/29/titleist-golf-ball-r-amp-d-team-answers-your-questions.aspx

Thanks for the info Eric. I was wondering how long they lasy as well. I have seral Prov1x box's and keep them on a shelf out of the sun in my office. I try to keep a dozed in my bag and refill as needed. Now that I know how lon they last I will purchase extras so I have a good backup supply. :-)