In one aspect, the invention relates to a pipette tip mounting shaft configuration and a disposable pipette tip having a matching configuration. The mounting shaft includes a locking section located above a lower sealing section. The locking section has outwardly extending locking lobes located above a stop member and a lower sealing section located below the stop member. In certain embodiments, the diameter of the mounting shaft below the stop member is reduced in order to lessen insertion and ejection forces, which is particularly helpful for hand-held multi-channel pipettors. In these embodiments, the lower sealing section contains either a frustoconical sealing section, or an annular groove and a sealing ring, such as a flouroelastomeric O-ring seal. When the mounting shaft is fully inserted into the collar of the mating disposable pipette tip, the tip locks onto the mounting shaft. The bore of the pipette tip includes a circumferential shelf or shoulder separating its upper collar from the tip sealing area which is located below the circumferential shelf. The tip collar preferably includes a locking ring located at or near the upper opening for the mounting shaft. The dimensions of the collar, and in particular the distance between its circumferential shelf and the locking ring, are selected to match the dimensions of the mounting shaft between the stop member and the upper end of the locking lobes, thus locking the pipette tip in a secure, reliable position and orientation while using ergonomic insertion and ejection forces. The locking lobes preferably include a ramp portion that gently flexes and distorts the pipette tip collar out of round as the mounting shaft is inserted in the pipette tip, rather than stretching the tip collar. The circumferential shelf on the pipette tip between the tip collar and the barrel isolates the sealing area at the upper end of the barrel from distortion, thus facilitating reliable sealing engagement between the lower sealing section of the mounting shaft and the sealing ring in the upper end of the barrel of the pipette tip.