European markets gained early Monday, with bank stocks rising as investors cheered the latest news on U.S. measures to prop up Citigroup.

The U.S. government has agreed to guarantee over $300 billion of Citigroup's troubled assets with conditions attached. As a result, the U.S. bank's shares were up over 40 percent in Frankfurt trade. CNBC's experts weigh in on what the Citi bailout means: