All passengers are still required to wear masks, though.
Back in October, Southwest said would start selling every seat on Dec. 1 and it's now doing so.
The decision comes after the carrier reported a record $1.2 billion third quarter loss because of the pandemic.
Southwest says it will notify passengers ahead of time if their flight has more than 65-percent of its seats sold.
Southwest was among the airlines who limited the number of seats for sale to promote social distancing onboard.
You can read Southwest's COVID-19 policy on their website.