TransGaming says The Sims 3: Generations expansion pack for Mac OS X (10.5.8 or higher) is now available for pre-order from the GameTree store for US$39.99. It’s scheduled for release on May 31.

Here’s how The Sims 3: Generations is described: “Start off in the imagination-fuelled world of childhood and embrace the drama of the teen years. Experience the complicated realities of adult life, then reap the benefits of growing up in each life stage. A wealth of new options and activities makes your Sims’ lives more meaningful than ever before, whatever their ages. With new celebrations, dramatic life events, and all-new ways for your Sims to express their creativity, The Sims 3 Generations lets your Sims live life to the fullest!”

The expansion pack requires The Sims 3 for the Mac to play. You won’t be able to activate/play The Sims 3 until it’s officially released.