Unless if you want to get eaten, the answer is yes! Realistically, the odds are in your favor. That being said, Yellowstone is a WILD place- and anything can, and does happen.
Please rent, rather than buy and throw out. You cannot fly with them in checked baggage or carry-on, they are incredibly difficult to recycle, and they are awful to have in our landfills.
If renting bear spray is financially prohibitive for you ($25/ can per week), let us know and we will find a solution for you to have bear spray while you are in Yellowstone. Your safety, and the bear’s safety, is of primary importance.