At a speed estimated by the pilot as 80 knots, he observed fluctuations in the oil pressure gauge of the port engine and he closed both throttles and abandoned the take-off. The tail of the aircraft was well off the ground at this stage, the pilot therefore attempted to lower the tail but the aircraft became airborne for a short period. He then took control action to return first the mainwheels and subsequently the tail wheel to the runway. When all three wheels were on the ground, heavy braking was applied but the aircraft over-ran the runway, continued through the prepared over-run area and finally ran into a creek some 180 metres beyond the sealed end of the runway.