James Ellison has moved to the top of the times in a delayed wet FP3 which saw an 80-minute suspension after oil was dropped on track which required an extensive clean up.
The JG Speedfit Kawasaki rider led Friday's fastest rider Christian Iddon at the chequered flag with a 1m 49.872s – some 13 seconds off yesterday's pace due to the wet conditions after heavy overnight rain drenched the Assen circuit.
After a tentative start to the session it was red flagged by 12 minutes as Tommy Bridewell's Bennetts Suzuki leaked oil on the track between the start/finish straight and turn three. The spill required an extensive clean which saw track action suspended for 80 minutes.
At the resumption a host of riders traded top times with Showdown contender Ellison going top from Iddon with Buildbase BMW's Richard Cooper in third.
BSB championship leader Shane Byrne, who opted only run a handful of laps in the slippery conditions, jumped to fourth late on ahead of Be Wiser Ducati team-mate Glenn Irwin.
Fellow title rivals Jason O'Halloran and Leon Haslam ended the session sixth and seventh respectively with Team WD-40 Kawasaki's Josh Hook setting an impressive pace in the wet.
Three-time Ryuichi Kiyonari produced a positive showing on the Smiths BMW to take ninth ahead of Michael Laverty who completed the top ten ahead of qualifying.