In January, CBO had issued a report with similar estimates, which were based on a bill passed by Congress in 2015, which was vetoed by then-President Barack Obama.
Like that report, the new CBO analysis is almost certain to make it politically difficult, if not impossible, for Republican Congressional leaders to pass a repeal bill without having a replacement bill in hand at the same time. The CBO has not yet issued a report on the leading Senate bill to replace Obamacare, which does not have enough GOP senators to pass at the moment.
The CBO's new report projected that a repeal-without-replacement would lead average premiums in the individual health insurance market to rise by about 25 percent relative to the current Obamacare law next year.
That increase "would reach about 50 percent in 2020, and premiums would about double by 2026," the CBO report found. Those premium hikes would occur in the "non-group market," or the private insurance market that serves people who do not get insurance through an employers.
And CBO said that "about half of the nation's population would live in areas having no insurer participating in the nongroup market in 2020 because of downward pressure on enrollment and upward pressure on premiums."
"That share would continue to increase, extending to about three-quarters of the population by 2026," the report said.
CBO also said that repealing many provisions of the Affordable Care Act, as Obamacare is formally known, would decrease federal deficits by $473 billion from 2017 through 2026.
Republican leaders in the Senate have unsuccessfully struggled for weeks to pass a bill that would replace large parts of Obamacare, and a frustrated President Donald Trump in reaction suggested Monday that Obamacare be repealed outright.
The Senate next week expects to consider a bill to either replace Obamacare, or repeal it, and then allow a replacement to be crafted later.
During a lunch meeting Wednesday, Trump pushed Senate Republicans to forge an agreement on health-care legislation before leaving town for the August recess.
"We have to stay here. We shouldn't leave town, and we should hammer this out and get it done," the president said.
Sen. Tom Carper, D-Del., said, in reaction to the CBO report, said, "Repealing the Affordable Care Act without a replacement plan would have disastrous effects on people's lives and our health care system."
"This course of action is just a hasty and reckless attempt by Republican leadership to make good on a campaign slogan when, instead, we should focus on working together across party lines to do what President Trump has said time and time again he wants to do: provide better health care at a lower cost for every American," Carper said.
Click here for more coverage of efforts to repeal the Affordable Care Act.