How is the capital gain on shares decided at time of sale?

Q.

I have had a number of Australian shares for some years. In that time I have participated in DRPs. How is the capital gain on shares decided in that instance and more particularly what about if you only sell some of the shares - is the price for shares in DRP bought first taken into account or is the whole parcel averaged to decide capital gains?

You, or your accountant, should have a record of the date and price of each purchase. When you sell, you can elect which shares are to be part of the selling parcel.