"For approximately three decades, these corporate giants dealt on an informal basis," Kleinberg wrote in his decision. "Even when the financial consequences were in the billions, they shared resources, worked together, supported mutual customers, and with only a handful of exceptions did so without a written contract."

HP had "every reason to believe" the settlement agreement "was consistent with 'business as usual,'" Kleinberg added.

Overall, Oracle's statements amounted to a valid contract and the company is required to continue porting its products to HP's Itanium servers at no cost to HP, the judge ruled.

Those products constitute the list of software products that were offered on HP Itanium platforms as of Sept. 20, 2010, "including any new releases, versions or updates of those products," Kleinberg added.

Oracle is obligated to continue the ports until HP stops selling Itanium-based servers, the judge wrote.