That's the trouble with these kinds of things; there's never any hard and fast proof - everything is anecdotal. If the mere presence of pellets of tin and/or lead in the petrol tank could solve the problems, grow your hair back and make you win the Lottery, don't you think the giant fuel companies and/or the motor car makers would be all over it? Of course, Dr David Locke, Broquet and all the other proponents of this are lucky they haven't been "disappeared" by the giant petro-chemical companies to protect their profits. I've found one fuel additive that actually works, but it's not for extra mileage, performance or anything like that, all it does is slowly clean the carbon off the backs of the valves and the piston crown / combustion chamber. It's made by Chevron and already in Texaco petrol. You can buy it in more concentrated form as Techron. There are others available too. Unlike the nebulous claims for other additives, Techron (or PEA) is actually provable. The other great additive for fuel economy is a vacuum gauge.