HP will distribute and provide support for Solaris on its ProLiant server and blade platforms and the two companies will also work on integrating Solaris 10 with HP's Insight software.
Sun previously signed Solaris distribution deals with IBM and Dell in 2007.
"This agreement represents a very important milestone for our customers," said Mark Potter, HP's senior vice president and general manager, BladeSystem and Insight software.
HP users who want to use Solaris on ProLiant will now have "a single point of purchase and accountability," he said.
However, the new Solaris agreement does not pertain to HP's Integrity line of servers, where HP's HP-UX operating system "remains the preferred Unix operating environment to address customers' mission-critical computing requirements," according to a statement.
Nonetheless, the deal "dramatically expands the available market for Solaris," said John Fowler, executive vice president of Sun's systems division.
The pact will have no effect on HP's deals with other vendors, Potter said. "We've always been about providing choice [for customers]. This is really about elevating Solaris to a strategic platform."
Solaris could no doubt benefit from the new partnership as it battles for share against Windows and Linux. But in turn, HP may simply have been hewing to market forces, according to one observer.
"This was largely about pragmatism," said Stephen O'Grady, an analyst with Redmonk. "There are a lot of HP customers that want to run Solaris."
As the recession continues, "you're going to see a fair amount of this type of interplay and interchanges [between vendors]," O'Grady added. "Particularly in a tough economic environment, customers are very empowered. They're going to demand certain things in their suppliers. One of those things is to work with the platforms and operating systems of their choice."