I have a 2010 Toyota Prius that I started driving in March 2010. I have kept a diary of all of the gas purchase with average mpg and gas costs. In the begining I was getting 53-65 MPG. when I was about to hit 10,000 miles it dropped to 43 and now I am getting 36MPG. I know the weather has changed, but the biggest change to my driving is that I drive shorter distances more often. In Vermont I was driving 26 miles straight. Now I drive maybe 5-10 mile trip. When I got the vehicle I was told I could use regular oil. The local toyota dealer told me to use synthetic and my mileage would improve. I called toyota b/c I think they owed me an oil change. I changed my oil every 5000 miles but was told synthetic would be opitimal. I will answer any and all question. I just want to know why I am getting such bad mileage in the city and get better mileage on the high way..