If you are a Mac, don’t wish to install Windows on your machine whatsoever. Thanks to arithine @2K forums, we have a guide which you can follow to successfully run the Civilization V on Mac OS. Current OS tested is Snow Leopard but the theory applies.
How to Play Civilization V on Mac
Install it, drag the application to folder you want steam in.
Open the application and log into steam.
Download the game, full version game or demo.
After you have downloaded, go to your library and hit “play game” when given the option, select Directx9.
Once in the game go to the graphics option and set it to windowed mode.
Play and Enjoy.
When you start up the game again, you need to go and change the game from windowed back to full-screen and then to windowed again. You can use steam launch options for that.
The fog of war does not show clouds, in minimum it is black raised hexes and at high settings, its just grayed out.
The mouse is not entirely accurate, keep an eye out for which button is glowing, not just on what your mouse is over.
Source: 2K Games Forum