Opera Software used to run its own root store program, but as of fall 2013, it no longer does so. Opera Software continues to take an active part in work to standardize the processes that safeguard the integrity and credibility of security certificates.
Newer versions of Opera (14 and higher) use the root store provided by the operating system and the list of EV-enabled roots maintained by Google. Older versions of Opera (versions 9.5 through 12) use Opera's online root store. Until fall 2013, the online solution was built on Opera's root store program, but after that it is based on NSS by Mozilla.
To get certificates to be accepted by Opera, roots should be part of the above-mentioned root store programs.