Not really answering the question there. Castrol GTX3 was a mineral base oil, whereas Mobil 1 is a fully synthetic. The price range is completely different and does not really help the OP out if he is wanting something like Castrol GTX3. On topic K8Canb, it appears Castrol have dropped the GTX3 and simply replaced the naming with their GTX Modern Engine range. Having a look at the specifications for the oil, the newer GTX Modern Engine oil meets and exceeds the specification of the GTX3 oil. So in that case, if you can't find any left over stock of the GTX3, you would be fine moving to the GTX Modern Engine. For further information, you can compare the two here: GTX 3: http://www.castrol.com/liveassets/bp_internet/castrol/castrol_australia/STAGING/local_assets/downloads/g/GTX3_B1768_04.doc GTX Modern Engine: http://www.tds.castrol.com.au/pdf/9981_GTX_15W-40_467161_2010_09.pdf Thanks for informative reply DJKOR. I was also considering Penrite which is 50% mineral oil and 50% synthetic. My car has done about 106000 kms and going for full synthetic may not be a good idea. Thanks again for the reply. K8canb