In the decommissioning project of tritium handling laboratories or/and facilities, oils such as used in the vacuum pumps have been left conventionally in their comprehensive facilities. Existence of oils, especially highly-contaminated with tritium, is becoming one of the serious problems in projects for decommissioning tritium handling laboratories because of no disposal way of the tritiated waste oils. Experiments using bubblers were carried out to examine the tritium contamination and decontamination of a volume of rotary-vacuum-pump-oil. Contamination of pump oil was observed by bubbling with tritiated water vapor and tritiated hydrogen gas. And then, subsequent decontamination of tritiated oil was processed by bubbling with pure water vapor and dry argon gas. The bubbling with water vapor was more effective than with the dry gas. Experimental results show that the water vapor bubbling in an oil bottle can remove tritium efficiently from the contaminated oil into another water-bubbling bottle.