Version 10.10 (Yosemite) or higher, Intel Core i3 2.2GHz, 4GB RAM, and an ATI Radeon 4850 / NVidia 640M or better.
Knowing the exact file size helps you plan your hard drive space. The Rising Tide expansion adds significant new assets: Version 10
Checking if your (like a newer M-series Mac) can run the game. Version 10.10 (Yosemite) or higher