On our first long trip (500 miles each way) in our '07 Camry Hybrid, we got 37.6 mpg stopping once after four hours on the road, with another four hours after the stop. There was no traffic. The drive involved ascending from sea level to 7,000 ft., and then down to 4,500 ft above sea level. We were driving in the desert up and down hills was at 75 miles per hour, and the temperature was HOT (above 90 F). On our way back, I thought we would get much better mpg because we would descend 7,000 ft. WRONG. There was no traffic and we drove (again) for four hours at a stretch before stopping for food. Again, it was hot. Even when driving down hills the gas engine was running. After we entered the Los Angeles area again and were driving at 65 miles per hour with much cooler outside temperatures, we still were using the gas engine on downhill stretches of the road. Usually, the needle enters the 60 mpg area when driving down hills, but not this time. The engine never was above the midpoint on the "Engine Temperature" guage. Was this poor performance because we had driven so long without stepping on the brake? Was it because the outside temperature had been so hot during most of our drive? Was it because most of our drive was at speeds exceeding 75 miles per hour? Overall, we still got 37.6 mpg on the entire trip, but I expected more. Does anyone have an answer?