Kaiser Permanente has 40 percent of California's lucrative health insurance market. A new report from Citigroup reveals Kaiser received more than $23 billion in premiums in 2011.
The report shows that just five health insurers control 91 percent of California's market.
Kaiser had the biggest share of the state's $59 billion health insurance business. Second place went to Anthem Blue Cross, which had 23 percent of the pie.
Blue Shield of California earned third place, followed by Health Net and UnitedHealth Group.
These insurers will be the biggest players in California's new health insurance exchange. That's an online marketplace where consumers will be able to compare plans and apply for federal subsidies. The Affordable Care Act requires everyone to have health insurance beginning next year.
State officials say California's exchange will be launched in the fall.
