NetSuite shares rose about 18 percent to $108.05 in morning trading, just shy of the offer price of $109 in cash per share.
Oracle shares were up slightly to $41.01.
"It's definitely pricey from Oracle's perspective, but it's understandable and it's justifiable especially in this environment, when we've seen software-as-a-service companies go as high as 10, 11, 12 times sales," said Morningstar analyst Rodney Nelson.
Oracle and NetSuite both offer software applications that help companies automate back end and administrative operations from technology to human resources.
Oracle's cloud business, which stores enterprise software and data on remote servers, lets the company sell to clients who lack the budget for on-site hardware and technology staff.
The deal could also help Oracle, which is aggressively trying to build and sell more cloud-based business software, play catch up with competitors such as Workday and Salesforce.com that specialize in cloud-based offerings.
Jefferies analysts said in a note the deal provides an immediate, significant entry into the mid-market for corporate applications, but also said "the price paid seems steep."