System Requirements:

Windows
OS: Windows® XP Processor: 2GHz Dual Core Processor (Intel® Core 2 Duo or AMD Athlon™ X2) or higher Memory: 2GB System RAM or more Graphics: 320MB Video RAM GPU w/ Shader Model 3.0 support. NVIDIA® GeForce® 8800 series or better. ATI Radeon™ HD3800 series or better DirectX®: 9.0c Hard Drive: 10GB Sound: 100% DirectX® 9.0C compliant sound card or equivalent onboard sound Co-Op Play:NVIDIA® GeForce® 8800 cards require 640MB of Video RAM. ATI Radeon™ HD3800 cards require 1GB of Video RAM
Mac
OS: Ubuntu 14.04.3 LTS, Ubuntu 15.04, Linux Mint 17.1, Steam OS Brewmaster CPU: Intel Core i5-4570T (2.9 GHz) or equivalent or AMD Athlon II X2 270 (3.8 GHz) or equivalent GPU:GeForce GT 630 (1024 MB) or equivalent or Radeon HD 6850 (1024 MB) or equivalent Recommended Graphics Drivers: Nvidia: 352, 355 or 358 series driver / AMD: AMD Catalyst (fglrx) 15.9 or better. MESA drivers and Intel Graphics are not currently supported. RAM: 4096 MB Disk Space: Around 7 GB

System Requirements:

Windows
OS:Windows XP or Vista.
Processor: 2.0 GHz Intel Dual-Core Pentium IV or equivalent or AMD Dual-Core Athlon XP or equivalent
Memory: 1 GB system RAM
Graphics: 128MB 3D graphics card with Shader Model 3.0 support (i.e. 7600 NVidia card or better, ATI X1300 card or better)
DirectX Version: DirectX 9.0c
Sound: DirectX 9.0c compatible 16-bit sound card
Hard Drive: 15 GB of Hard Drive Space
Display: DirectX compatible display capable of 640x480 in 16-bit color
Linux
OS:Ubuntu 14.04.3 LTS, Ubuntu 15.04, Linux Mint 17.1, Steam OS Brewmaster
CPU: Intel Core i5-4570T (2.9 GHz) or equivalent or AMD FX-4300 (3.8 GHz) or equivalent
Memory: 4096 MB
GPU: GeForce GTX 460 (1024 MB) or equivalent or Radeon HD 6850 (1024 MB) or equivalent
Recommended Graphics Drivers: Nvidia: 352, 355 or 358 series driver / AMD: AMD Catalyst (fglrx) 15.9 or better. MESA drivers and Intel Graphics are not currently supported.
Hard Drive: Around 7 GB
Disclaimer: Due to issues surrounding the original engine, some stuttering may be observed during gameplay. These types of streaming issues may be improved with faster HDD units.