For nearly the entire time I've owned my Camry, I've been tracking my gas purchases and fuel efficiency using a ThinkDB database on my PDA. Finally got around to exporting nearly 8 years worth of data into a spreadsheet for some analysis. The data is kind of interesting to look at.
Here's what gas prices have been doing over the past 8 years.
Almost hard to believe these days that gas was going for less than $1/gallon
Here's what the fuel efficiency looks like over the past 8 years
I chose to plot fuel efficiency in terms of gallons/100 miles, so lower numbers mean better fuel efficiency. I think the two spikes that get close to 7 and 8 gallons/100 miles are anomalies probably due to typos entering the data, so I'll ignore those. The average comes out to about 4.2 gallons/100 miles, which is pretty decent (just under 25 mpg). A lot of the noisiness in the first few years are due to frequent road trips. The graph smooths out toward the end because I just haven't been taking any long road trips with the Camry for the past few years. Where it starts smoothing out also coincides nicely with when we moved out of the apartment and into the house, and didn't have to spend time stuck in rush hour traffic on the James Island Connector anymore.
What kind of surprised me is that there really hasn't been much change in fuel efficiency over the years. I figured as the car got older, efficiency would go down a little, but there doesn't seem to be that upward trend in the data.
This next graph shows how much it costs to feed the car per mile.
Follows the graph of gas prices pretty closely (which is expected).
Over the entire reported period, the car has been driven about 87100 miles, consumed nearly 3500 gallons of gas which I spent close to $6900 on.