I bought this under the guidance of my Smog Technician to clear up a high NOx rating for 15mph.I have a 1998 Honda Civic EX VTEC, 5 speed. The past 15 years, the car has always passed smog with flying colors (usually, all the numbers are 0 or close to it). This year, the car passed everything fine with the same record, except NOx at 15 mph. Reading online said that this is the place to fail if your car is going to fail. Prior years, the number was 50, with a max limit of 480 or so. This year, it went up to 780.So, I bought seafoam and, unlike a lot of other people, my car hardly smoked at all. I baby my car usually (short shift, cruise at 60-65, easy on the gas and brake and clutch) all in the name of gas mileage. With only an intake, exhaust, and headers, I average into the mid 40's for gas mileage average, when the EPA for the car is 25/33.I'm not sure if this is something to do with my car getting old and the Catylitic converter is getting bad, but after Seafoam, the car registered a barely pass of 460 out of 480 max.For those of you who wonder, I added the seafoam through the brake booster vacuum line. This, from what I have been told, is good for a quick fix and to pass smog. I later dumped the rest of the can (2/3 left) into the gas tank. Its hard to notice, but I believe the car idles a bit easier (no gushing kind of noises). Could be cleaning the injectors.Whatever the case, I passed smog and plan on using this the next time I go in for a smog 2 years from now.I read a lot of forums online and there is great debate over seafoam. It took me a while to buy it, but it worked. 5 Stars! Worst that happens is you put it into a car that is held together by carbon deposits and your car leaks. If you car leaks oil already, or you believe it has the possibility to with engine cleaning, don't buy this. But if you have high NOx or other figures, this is is a good buy to pass smog. Heck, once you pass smog, it doesn't matter anymore for 2 years. Cheap investment/safety net for your car.