During 1953 some small-scale tests were made on the base injection of foam into petrol storage tanks (1). These tests, which were made in a 9 ft diameter by 30 ft high tank, with a depth of petrol from injection point to surface of approximately 27 ft, suggested that the properties of the foam at injection needed to be controlled within certain limits, if the petrol picked up by the foam at the surface should not exceed critical value of 10 per cent by volume, above which extinction could not be achieved. While these tests were a valuable pointer to the possibilties of using base injection, it was realised that the tests on a larger tank would be necessary, since the 9 ft diameter tank represented only some 1/250th of the petrol surface area present in the largest storage tanks. During 1958, Messrs. I.C.I. (Heavy Organic Chemicals) Ltd., made available a 45 ft diameter x 30 ft high petrol storage tank for further experiments, that is, a tank of 1/10th the free petrol surface area of the largest tanks in use. This has made possible a valuable extension of the original work and has given some further useful information and the effect of tank size on the petrol picked up by the foam.