Nate Silver from 538 crunches the numbers:

“After Democrat Doug Jones won a stunning victory in Alabama’s special election for the U.S. Senate last month, lots of smart people whose work I read and follow, such as The New York Times’s Nate Cohn, declared that the battle for Senate control in 2018 was a “toss-up.” Prediction markets largely concur; after Jones’s win, the betting odds of Democrats taking over the Senate shot up to about 45 percent.

I think this might be premature. Winning in Alabama certainly makes the Democrats’ path easier: They could now gain control of the Senate by retaining all of their own seats, plus picking up the Republican held-seats in purplish Nevada and Arizona. But they’re probably still the underdogs.
Democrats face a really tough Senate map.”
More at link:

https://fivethirtyeight.com/features/are-democrats-senate-chances-overrated/