Google’s Android operating system has been a cash cow for the company, if Oracle is to be believed. Android has thus far generated $31 billion for Google, Oracle claimed in a recent court filing that was reported by Bloomberg Thursday. $22 billion of those were profits for Google, according to the filing.

Google makes Android available for free to operators and phone manufacturers, but the company generates profits through advertising shown on Android phones as well as apps sold to users of its Google Play store. The company doesn’t publicly break out its Android revenue, but executives have long stressed the growing importance of mobile for Google’s bottom line.

Oracle’s disclosure comes as the two tech giants continue to fight over claims that Google used some of Oracle’s Java software to build Android without proper compensation. Google has long denied these claims, and argued in court filings that the disclosure of its Android revenue could have negative effect on its business, asking a judge to reseal related documents.