Michael and William Dunlop both enjoyed considerable practice success at the first session on Monday evening in good conditions.
Michael is top of the 1000cc and 600cc classes while William produced the fastest time for the 250cc.
In the big bikes, Michael recorded a speed of 109.4 mph, Ryan Farquhar was next with 108.8 mph and Ian Lougher was third with 108.38 mph.
In the 600cc, Michael Dunlop is well clear in the standings with 108.197 mph. Ryan Farquhar recorded a best of 105.57 mph and Ian Lougher averaged 104.79 mph.
William Dunlop leads the 250cc at 101.047 mph - then it's Barry Davidson at 97.98 mph and Castletown's Chris Palmer at 97.42 mph.
Ryan Farquhar is the quickest 650 at 99.145 mph.
Roy Richardson notched the quickest 400cc lap at 93.926 mph, just ahead of Alistair Haworth and Peter Simpson.
Lastly in the solos, Chris Palmer is fastest in the 125cc at 93.240 mph with William Dunlop and Sam Dunlop.
In the sidcar class, defending champions Ian and Carl Bell top the standings at 94.550 mph followed by double 2010 T.T. winners Klaus Klaffenbock/Dan Sayle and Greg Lambert/Aaron Gallagher.
There is more practice and the first two races of the 2010 Southern 100 meeting this evening with roads around the Billown Course closing at 6.05pm to 9.40pm at the latest.