The hotly debated individual health insurance mandate — a key piece of the Affordable Care Act that’s under Supreme Court review — would require that just about everyone in the United States have some type of medical coverage, whether the person is employed or not.

For now, companies continue to be the leading source of health insurance in the country, covering about 150 million people, according to the nonprofit Henry J. Kaiser Family Foundation, a Menlo Park-based health policy organization that’s not affiliated with Kaiser Permanente.

Each year, the nonpartisan foundation teams up with the Washington, D.C.-based Health Research & Educational Trust to survey more than 2,000 employers with the goal of highlighting important trends of employer-sponsored health benefits.

Here’s a look at the key findings from its most recent report, analyzing data from 2011.

PPOs still most popular. Nationally, PPOs are by far the most common plan type, enrolling 55 percent of covered workers. That compares with 17 percent of workers enrolled in an HMO and 17 percent enrolled in a high-deductible plan with a savings option. In the West, where HMOs are more popular, only 40 percent of workers are enrolled in a PPO.

Fewer firms offer health benefits. Sixty percent of firms offered health benefits to their workers in 2011, down from 69 percent in 2010. Among firms with three to nine employees, 48 percent offer health benefits — consistent with recent years.

Costs shift to workers. Twenty-three percent of firms offering health benefits gave employees the option to enroll in a high-deductible health plan with a savings option, up from 15 percent in 2010. This type of plan, which was nonexistent in 2005, is becoming more common as employers seek affordable coverage and look to shift higher medical costs to workers.

Incentives to be well. In an effort to improve health and lower costs, most employers offer some type of wellness program. Fourteen percent of those firms also offer gift cards, travel, merchandise or cash to workers who participate in the program.