The simple answer is no. You can play at an online casino that offers Instant Play for fun, or casinos that offer practice play for fun. In both cases, with the exception of Bodog Casino where you can immediately load and play a practice game, you have to register as a guest. This type of registration does not require a deposit. However, not joining a casino means you are missing out on a wide variety of exciting bonuses including: Welcome Bonuses (some as high as $20,000), daily and weekly bonuses, tournaments, rewards, VIP Programs, and more.
