Warning: Avoid third-party "direct download" websites offering standalone .exe files for Rising Tide. Because the expansion requires Steam DRM and the base game, any such file is almost certainly pirated, malware-ridden, or non-functional.
You cannot buy a physical disc for this expansion that works offline. Rising Tide requires the Steam client for installation, authentication, and patches. You must download it via the Steam store or an authorized key reseller. You cannot buy a physical disc for this