This link was sent to me and I was dubious - but you get a full money back guarantee so I thought what the heck. The website says you'll save 15% to 27%, but I have to say that my husband and I have found a 10% reduction - still good. You can get them on
www.fuelsaver.ie, the price is in dollars but there's someone here in Ireland distributing because we got ours four days after purchase with an Irish postmark. We've noticed benefits ... may be worth a try.