The first results from the Senate 2018 campaign, using Congress Infinity‘s sim mode, are in. Note the campaign has not been finalized.
Republican majorities: 97%
Democratic majorities (includes independents who caucus with the Democrats): 1%
Which means, since Pence is the tie-breaking vote in a 50-50 Senate, Republicans have an effective majority 99% of the runs.
Overall average seats: Republicans 53.9, Democrats 46.1.
Republicans gained a super-majority (60 or more seats) 1% of the time, at 60 seats.
The Democrats’ best result was 51 seats, again 1% of the time.