Pick the basil leaves when they are full and green. Place the leaves into the strainer and rinse them off well in your sink.
Lay the leaves on a paper towel and pat them dry.
Place the whole leaves into a plastic freezer bag and place them in your freezer. Put only a small number of leaves per bag so they have room to freeze.
Chop the basil up into small pieces and mix it with 2 tsp. of olive oil for every 1/4 cup of basil. Place the mixture into a plastic container and place them into the freezer. Alternately, freeze small portions of the mixture on a tray, then put them in a plastic freezer bag to have ready-measured portions to use when cooking.