Enough insurers are planning to sell coverage on the Affordable Care Act's insurance exchanges next year to keep them working — if only barely — in most parts of the country.

Competition in many markets has dwindled to one insurer — or none in some cases — and another round of steep price hikes is expected to squeeze consumers who don't receive big income-based tax credits to help pay their bill.

"What we're seeing is a deterioration in these markets, but the markets haven't imploded, they haven't gone into a rapid downward decline," said Dan Mendelson, president of the consulting firm Avalere...