Abstract: The present invention consists in a mixing apparatus for mixing two flowable substances, and preferably oil and petrol, in a desired volumetric ratio. The apparatus includes a first container of predetermined volume and a second container of predetermined volume. These containers have a closable filling means through which the first container can be filled with a first flowable substance and the second container can be filled with a second flowable substance. There is a passage between the containers and a valve means operable to close the passage when the second container is being filled but operable to open the passage, whether or not the second container is filled, when the first container is being filled when the valve means opens the contents of the two containers can pass through the passage and be mixed together.